Communicating channel state information (csi) of multiple transmission points

ABSTRACT

Embodiments contemplate methods and systems for determining and communicating channel state information (CSI) for one or more transmission points (or CSI reference signal resources). Embodiments further contemplate determining transmission states may include applying at least one CSI process for channel state information (CSI) reporting. Embodiments also contemplate aperiodic and/or periodic reporting of one or more report types (e.g., rank indicator (RI)) of CSI, perhaps based on one or more reporting modes that may be configured for each of the one or more CSI process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/655,359, filed Jun. 4, 2012, titled “COMMUNICATING CHANNEL STATEINFORMATION (CSI) OF MULTIPLE TRANSMISSION POINTS”, and U.S. ProvisionalApplication No. 61/678,559, filed Aug. 1, 2012, titled “COMMUNICATINGCHANNEL STATE INFORMATION (CSI) OF MULTIPLE TRANSMISSION POINTS”, thedisclosures of both applications hereby incorporated by reference hereinin their respective entirety, for all purposes.

BACKGROUND

A wireless communication system may be evaluated based on the system'saverage cell throughput and/or its cell-edge throughput. Cell-edge usersmay experience low received signal strength and the cell edgeperformance may be affected by inter-cell interference (ICI). This maybe true for systems designed to operate with a frequency reuse factor ofone or close to one. Such frequency re-use may imply that systems maybecome interference limited as many or all cells may transmit on many orall time and frequency resources simultaneously. Additionally, powerboosting may not improve cell-edge performance as both the serving cellsignal and the interfering signal strengths may be increased.

SUMMARY

A detailed description of illustrative embodiments will now be describedwith reference to the various Figures. Although this descriptionprovides a detailed example of possible implementations, it should benoted that the details are intended to be exemplary and in no way limitthe scope of the application. As used herein, the article “a”, absentfurther qualification or characterization, may be understood to mean“one or more” or “at least one”, for example.

Embodiments contemplate methods and systems for communicatingtransmission states or CSI processes. For example, a method fordetermining transmission states or CSI processes may include applying atleast one transmission state or CSI process parameter to channel stateinformation (CSI). The method may also include reporting CSI based on atransmission state or CSI process and at least one transmission state orCSI process parameter applied thereto, and applying a correction factorto the at least one transmission state or CSI process.

Embodiments contemplate a wireless transmit/receive device (WTRU) thatmay be configured, at least in part, to identify one or moretransmission points. The one or more transmission points may beconfigured for channel state information (CSI) reporting. The WTRU maybe further configured to generate CSI for the one or more transmissionpoints. Also, the WTRU may be configured to send the CSI to one or morenodes in communication with the WTRU. Embodiments contemplate that theone or more transmission points may include at least one antenna port incommunication with the WTRU. Embodiments also contemplate that the oneor more transmission points may be CSI reference signal (CSI-RS)resources.

Embodiments contemplate one or more methods that may be performed by awireless transmit and receive unit (WTRU). One or more embodiments mayinclude identifying K transmission points, where the K transmissionpoints may be configured for channel state information (CSI) reporting,and where K may be an integer. Embodiments may further includegenerating CSI for one or more of the K transmission points. Inaddition, embodiments may include sending the CSI to one or more nodesin communication with the WTRU. Also, embodiments may include receivingat least one of a CSI reference signal (CSI-RS) or a common referencesignal (CRS) that may be transmitted respectively by the K transmissionpoints. Embodiments may include identifying the K transmission pointsbased, at least in part, on the received CSI-RS or CRS. In one or moreembodiments, the generating the CSI may include generating at least oneof a joint rank indication or a per-point rank indication for the one ormore of the K transmission points. In one or more embodiments, thegenerating the CSI may include generating a joint channel quality index(CQI), where the joint CQI may correspond to a joint transmission overthe one or more of the K transmission points.

Embodiments contemplate a wireless transmit/receive device (WTRU) thatmay be configured, at least in part, to identify one or moretransmission points, where the one or more transmission points may beconfigured for channel state information (CSI) reporting. The WTRU maybe configured to determine a transmission state or CSI process for theone or more transmission points. The WTRU may be configured to generateCSI for the one or more transmission points. The WTRU may be furtherconfigured to receive an indication of the transmission state or CSIprocess for the respective one or more transmission points, where theindication of the transmission state or CSI process may include one ormore of a transmitting state, an interfering state, a blanked state, oran unknown state, for example. The WTRU may be further configured tocompare the determined transmission state or CSI process for the one ormore transmission points to a predetermined transition state or CSIprocess for the one or more transmission points. The WTRU may also beconfigured to send the CSI for respective one or more transmissionpoints to one or more nodes in communication with the WTRU upon thetransmission state or CSI process of the respective one or moretransmission points being in the predetermined transmission state or CSIprocess.

Embodiments contemplate one or more methods to configure a WTRU tocalculate CQI for multiple Transmission States or CSI Cases or CSIProcesses. Embodiments also contemplate one or more methods to linknon-zero-power channel state information reference signals (NZP CSI-RS)in the CoMP Resource Management Set to NZP CSI-RS in the CoMPMeasurement Set. Embodiments also contemplate one or more methods toconfigure a WTRU with a primary Transmission State or CSI Case or CSIProcess, for fallback, default and/or highest priority. Embodiments alsocontemplate one or more methods to select physical uplink controlchannel (PUCCH) Format 3 resources for CSI feedback and A/N of multipleCSI Processes. And embodiments contemplate one or more methods totrigger measurement reports out-of-coordinating cluster points to limituplink (UL) interference.

Embodiments contemplate a wireless transmit/receive unit (WTRU) that maycomprise a processor. The processor may be configured with one or morechannel state information (CSI) processes. The processor may beconfigured to receive an indication in a CSI request field. Theindication may indicate at least one of the one or more CSI processes.The processor may also be configured to generate a periodic reportand/or an aperiodic report corresponding to the at least one of the oneor more CSI processes. The processor may also be configured to send theperiodic report and/or aperiodic report via a physical uplink sharedchannel (PUSCH).

Embodiments contemplate a wireless transmit/receive unit (WTRU). TheWTRU may be in communication with one or more serving cells. The WTRUmay comprise a processor. The processor may be configured with one ormore channel state information (CSI) processes for each the one or moreserving cells. The processor may be configured with a period for a setof subframes. Also, the processor may be configured with an offset forthe set of subframes. The processor may be configured to generate afirst periodic report and/or a first aperiodic report corresponding to afirst CSI process of the one or more CSI processes and a first servingcell of the one or more serving cells. And the processor may beconfigured to send the first periodic report and/or a first aperiodicreport on the set of subframes via a physical channel including at leastone of a physical uplink control channel (PUCCH) or a physical uplinkshared channel (PUSCH).

Embodiments contemplate a wireless transmit/receive unit (WTRU) that maycomprise a processor. The processor may be configured at least with oneor more channel state information (CSI) processes. The processor mayalso be configured with a rank indicator (RI) associated with a firstCSI process of the one or more CSI processes. The RI may be configurableto be associated with one or more CSI processes in addition to the firstCSI process. The processor may be configured to at least associate theRI with at least a second CSI process. The processor may be configuredto report a common RI value. The common RI value may be the RIassociated with the first CSI process and the at least second CSIprocess.

Embodiments contemplate a wireless transmit/receive unit (WTRU). TheWTRU may comprise a processor. The processor may be configured with oneor more channel state information (CSI) processes. The processor mayalso be configured with one or more types of feedback reportscorresponding to the one or more CSI processes. The processor may beconfigured to generate a first periodic report and/or a first aperiodicreport corresponding to a first CSI process of the one or more CSIprocesses. The first periodic report and/or the first aperiodic reportmay also correspond to a rank indicator (RI) report type of the one ormore report types. The processor may be configured to generate a secondperiodic report and/or a second aperiodic report corresponding to asecond CSI process of the one or more CSI processes. The second periodicreport and/or the second aperiodic report may correspond to the RIreport type of the one or more report types. The processor may also beconfigured to send the first periodic report and/or the first aperiodicreport and the second periodic report and/or the second aperiodicreport. The processor may also be configured to drop one of the firstperiodic report and/or the first aperiodic report or the second periodicreport and/or the second aperiodic report upon a collision between thefirst periodic report and/or the first aperiodic report and the secondperiodic report and/or the second aperiodic report. The first periodicreport and/or the first aperiodic report and the second periodic reportand/or the second aperiodic report may include an RI value applicable toboth the first periodic report and/or the first aperiodic report and thesecond periodic report and/or the second aperiodic report.

Embodiments contemplate a wireless transmit/receive unit (WTRU) that maycomprise a processor. The processor may be configured at least with oneor more channel state information (CSI) processes. The processor may beconfigured to at least assume at least one of a physical downlink sharedchannel (PDSCH) transmission power for each of the one or more CSIprocesses, or a different ratio of PDSCH energy per resource element(EPRE) to CSI EPRE for each of the one or more CSI processes.

Embodiments contemplate an evolved node-B (eNB), where the eNB may be incommunication with a wireless transmit/receive unit (WTRU). The eNB maycomprise a processor. The processor may be configured to provide aconfiguration to the WTRU. The configuration may include one or morechannel state information (CSI) processes. The configuration may alsoinclude a CSI request field. An indication associated with the CSIrequest field may indicate at least one of the one or more CSIprocesses. The processor may also be configured to receive a periodicreport and/or an aperiodic report corresponding to at least one of theone or more CSI processes from the WTRU via a physical uplink sharedchannel (PUSCH).

Embodiments contemplate an evolved node-B (eNB) that may be incommunication with a wireless transmit/receive unit (WTRU). The WTRU maybe in communication with one or more serving cells. The eNB may comprisea processor. The processor may be configured to provide the WTRU with aconfiguration. The configuration may include one or more channel stateinformation (CSI) processes for each of the one or more serving cells.The configuration may include a period for a set of subframes. Theconfiguration may also include an offset for the set of subframes. Theprocessor may be configured to receive a periodic report and/or anaperiodic report corresponding to at least one of the one or more CSIprocesses on the set of subframes from the WTRU via a physical uplinkcontrol channel (PUCCH).

Embodiments contemplate an evolved node-B (eNB) that may be incommunication with a wireless transmit/receive unit (WTRU). The eNB maycomprise a processor. The processor may be configured to at leastprovide the WTRU with a configuration. The configuration may include atleast one or more channel state information (CSI) processes. Theconfiguration may also include a rank indicator (RI) associated with afirst CSI process of the one or more CSI processes. The RI may beconfigurable to be associated with one or more CSI processes in additionto the first CSI process. The processor may also be configured toreceive a report including a common RI value from the WTRU. The commonRI value may be the RI associated with a first CSI process and at leasta second CSI process.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of disclosed embodiments may bebetter understood when read in conjunction with the appended drawings.For the purposes of illustration, there is shown in the drawingsexemplary embodiments; however, the subject matter is not limited to thespecific elements and instrumentalities disclosed. In the drawings:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 illustrates an example periodic feedback reporting sequenceconsistent with embodiments;

FIG. 3A illustrates example channel state information reference signal(CSI-RS) port mappings for normal CP subframes consistent withembodiments;

FIG. 3B illustrates an example four resource element set consistent withembodiments;

FIG. 4 illustrates an example wireless device configuration consistentwith embodiments;

FIG. 5 illustrates an example method consistent with embodiments; and

FIG. 6 illustrates an example wireless device configuration consistentwith embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like. As shown in FIG. 1A, the communicationssystem 100 may include wireless transmit/receive units (WTRUs) 102 a,102 b, 102 c, 102 d, a radio access network (RAN) 104, a core network106, a public switched telephone network (PSTN) 108, the Internet 110,and other networks 112, though it will be appreciated that the disclosedembodiments contemplate any number of WTRUs, base stations, networks,and/or network elements. Each of the WTRUs 102 a, 102 b, 102 c, 102 dmay be any type of device configured to operate and/or communicate in awireless environment. By way of example, the WTRUs 102 a, 102 b, 102 c,102 d may be configured to transmit and/or receive wireless signals andmay include user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a smartphone, a laptop, a netbook, a personal computer,a wireless sensor, consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it will be appreciated that the basestations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA20001×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managementgateway (MME) 142, a serving gateway 144, and a packet data network(PDN) gateway 146. While each of the foregoing elements are depicted aspart of the core network 106, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 142 may be connected to each of the eNode-Bs 142 a, 142 b, 142 cin the RAN 104 via an Si interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the Sl interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

In order to support higher data rate and spectrum efficiency, amongother rationale, the Third Generation Partnership Project (3GPP) LongTerm Evolution (LTE) system has been introduced into 3GPP Release 8 (R8)(LTE Release 8 may be referred to herein as LTE R8 or R8-LTE). In LTE,transmissions on the uplink may be performed using Single CarrierFrequency Division Multiple Access (SC-FDMA). In particular, the SC-FDMAthat may be used in the LTE uplink may be based on Discrete FourierTransform Spread Orthogonal Frequency Division Multiplexing (DFT-S-OFDM)technology. As used herein, the terms SC-FDMA and DFT-S-OFDM may be usedinterchangeably.

In LTE, a wireless transmit/receive unit (WTRU), alternatively referredto as a user equipment (UE), may transmit on the uplink using limited,contiguous set of assigned sub-carriers in a Frequency Division MultipleAccess (FDMA) arrangement, and in some embodiments perhaps only alimited, contiguous set of assigned sub-carriers in a Frequency DivisionMultiple Access (FDMA) arrangement. For example, if the overallOrthogonal Frequency Division Multiplexing (OFDM) signal or systembandwidth in the uplink is composed of useful sub-carriers numbered 1 to100, a first given WTRU may be assigned to transmit on sub-carriers1-12, a second WTRU may be assigned to transmit on sub-carriers 13-24,and so on. While the different WTRUs may each transmit into a subset ofthe available transmission bandwidth, and perhaps may each may transmitinto only a subset of the available transmission bandwidth, an evolvedNode-B (eNodeB) serving the WTRUs may receive the composite uplinksignal across the entire transmission bandwidth.

LTE Advanced (which includes LTE Release 10 (R10) and may include futurereleases such as Release 11, also referred to herein as LTE-A, LTE R10,or R10-LTE) is an enhancement of the LTE standard that provides afully-compliant 4G upgrade path for LTE and 3G networks. In LTE-A,carrier aggregation may be supported, and, unlike in LTE, multiplecarriers may be assigned to the uplink, downlink, or both.

Embodiments recognize that coordinated multi-point operation (CoMP) inthe downlink may refer to a set of possible schemes whereintransmissions from multiple geographically separated transmission pointsmay be coordinated to improve system performance in terms of cell-edgethroughput and/or system throughput. Examples of such schemes includeJoint Transmission, wherein multiple points may simultaneously transmitinformation intended for a WTRU; Dynamic Point Selection, wherein one ofa set of points may be dynamically selected for transmission to a WTRU;and Coordinated Scheduling/Coordinated Beamforming, wherein interferencetowards a WTRU being scheduled from a first point may be avoided byproper coordination of interfering transmissions from a second point.

In both LTE and LTE-A, as well as other wireless systems, systemperformance may be evaluated based on average cell throughput and/orcell-edge throughput. While average cell throughput performance can beimproved by increasing the received signal strength using power boostingtechniques, the cell-edge users may experience low received signalstrength and the cell edge performance may therefore be primarilyaffected by inter-cell interference (ICI). This may be especially truefor the systems designed to operate with a frequency reuse factor of oneor close to one, which is contemplated by OFDM-based 4G networks.

Embodiments contemplate that a wireless system may be evaluated based onits average cell throughput and/or its cell-edge throughput. Embodimentscontemplate the improvement of the cell average and/or cell-edgeperformance. Average cell performance may be improved by increasing thereceived signal strength using power boosting techniques. However, thecell-edge users may experience low received signal strength and the celledge performance may therefore be affected by inter-cell interference(ICI). This may be especially common in systems designed to operate witha frequency reuse factor of one or close to one, which may beimplemented by OFDM-based 4G networks. Such frequency re-use may resultin systems that become especially interference limited when many or allcells transmit on many, or perhaps all, time and frequency resourcessimultaneously. Embodiments recognize that power boosting may notimprove cell-edge performance, perhaps because both the serving cellsignal and the interfering signal strengths may be increased, which mayin turn increase ICI, for example.

Embodiments contemplate other techniques that may be used to improvecell-edge performance, such as coordinated multi-point (CoMP)transmission and reception. In multi-point transmission and receptionembodiments, transmission or reception from antennas not in “closeproximity” may be implemented, where “close proximity” may be a distancebeyond the spacing of a few wavelengths such that most antennas, orperhaps all antennas, may be subject to different long-term fading. Insuch a transmission mode, several cells or transmission points maycombine to improve the received Signal-to-Interference-Noise-Ratio(SINR) at a WTRU.

Embodiments contemplate that the term “serving cell” may be used for asingle cell transmitting Physical Downlink Control Channel (PDCCH)assignments, for example, as defined in LTE R8 (a single cell).Embodiments also contemplate that several CoMP categories may be used,including joint processing (JP), where the data may be available at eachpoint in a CoMP cooperating set. In JP embodiments, joint transmission(JT) may be used, where Physical Downlink Shared Channel (PDSCH)transmissions may be sent from multiple points, such as part of a CoMPcooperating set, or perhaps an entire CoMP cooperating set, at one time.Data to a single WTRU may be simultaneously transmitted from multipletransmission points, for example, to (coherently or non-coherently)improve the received signal quality and/or actively cancel interferencefor other WTRUs. Also embodiments contemplate that in JP, dynamic cellselection may be used, where PDSCH transmissions may be sent from onepoint within a CoMP cooperating set at one time, for example.

Another CoMP category may be coordinated scheduling/coordinatedbeamforming (CS/CB), where the data may be available at the serving cell(i.e., data transmission is only performed from that point), and in someembodiments may only be available at the serving cell, but userscheduling/beamforming decisions may be made with coordination amongcells corresponding to a CoMP cooperating set.

Embodiments contemplate that at least one CoMP category may include cellaggregation. Some transmission points or each transmission point mayhave independent data to transmit to the WTRU on the same carrierfrequency. Some cells or each cell may have its own data and/or signalflow to and from the WTRU. For example, some cells or each cell may useindependent HARQ processes.

Embodiments contemplate that one or more CoMP sets may include a CoMPcooperating set, where a set of geographically separated points aredirectly or indirectly participating in PDSCH transmission to a WTRU.This set may or may not be transparent to a WTRU. Another CoMP set maybe CoMP transmission point(s), which may be a point or set of pointsthat may be actively transmitting PDSCH to a WTRU. The set of CoMPtransmission point(s) may be a subset of the CoMP cooperating set. In JTembodiments, CoMP transmission points may be the points in the CoMPcooperating set. For dynamic cell selection embodiments, a single pointmay be the transmission point in some subframes, or perhaps in everysubframe. This single transmission point may change dynamically withinthe CoMP cooperating set. For CS/CB embodiments, the CoMP transmissionpoint may correspond to a “serving cell”, for example.

Embodiments contemplate other CoMP sets that may include a CoMPmeasurement set that may be a set of cells for which channelstate/statistical information (related to their link to the WTRU) may bereported. In some embodiments, a CoMP measurement set may be the same asthe CoMP cooperating set. Actual WTRU reports may include feedback for asubset of cells of the CoMP measurement cells, and in some embodimentsmay only include feedback for a subset of cells of the CoMP measurementcells, which may be referred to as reported cells.

Embodiments contemplate that channel state information (CSI) feedbackmay be reported in the format of rank (e.g., rank indicator (RI)),precoder matrix index (PMI), and/or channel quality indicator (CQI),where PMI may be calculated at the WTRU by quantizing the channelagainst a pre-defined codebook, for example. CSI feedback may includeCQI/PMI/RI reports and may be provided on either a periodic or anaperiodic basis. Parameters that may be used to control the informationreported by the WTRU may be based on the system bandwidth and/or may beprovided in radio resource control (RRC) Connection Setup,Reconfiguration, and/or Reestablishment messages. The informationreported by a WTRU may vary based on the transmission mode, which may bedefined in the same RRC messages. Table 1 contains a summary ofexemplary reporting modes contemplated by embodiments.

TABLE 1 Exemplary Reporting Modes Transmission Mode Aperiodic FeedbackPeriodic Feedback 1: Port 0 Mode 2-0: UE selected sub band CQI: Mode1-0: WB CQI 2: Tx Diversity WB CQI + CQI over M best subbands. Mode 2-0:UE Selected sub band CQI: 3: Open Loop SM Mode 3-0: HL configured subband WB CQI +UE reports CQI in preferred (large delay CDD) CQI: WB CQI +sub-band CQI. sub-band in each BW part, one BW part (or Tx Diversity)Note-CQI for first CW only, No PMI in each reporting opportunity. 7:Port 5 Note-CQI for first CW only, No PMI (or port 0 or Tx Div) 8(without PMI): Port 7/8 (or single port or Tx Div): Release 9 only 4:Closed Loop SM Mode 1-2: WB CQI/Multiple PMI: CQI Mode 1-1: WBCQI/Single PMI (or Tx Div) for each CW; PMI for each sub-band. Mode 2-1:UE selected sub-band CQI/ 6: Closed Loop Rank 1 Mode 2-2: UE selectedsub band CQI/ Single PMI (N^(DL) _(RB) > 7 only): WB CQI/PMI + PrecodingMultiple PMI: CQI per CW and PMI, UE reports CQI in preferred sub-bandin (or Tx Div) both over full BW and M best sub- each BW part bands. 8(with PMI): Port 7/8 Mode 3-1: HL configured sub band (or single port orTx CQI/Single PMI: WB CQI + sub-band Div): Release 9 only CQI, both perCW. 5: MU-MIMO Mode 3-1: HL configured sub band (or Tx Div) CQI/SinglePMI (see above)

Embodiments contemplate that periodic feedback may be transmitted on thePhysical Uplink Control Channel (PUCCH) channel, although it may be senton the Physical Uplink Shared Channel (PUSCH) channel when that channelexists. Periodic reporting may use a sequence of one or more differenttypes of reports. Such types may include “Type 1” that may reportsub-band CQI, “Type 2” that may report wideband CQI/PMI, “Type 3” thatmay report RI, and “Type 4” that may report wideband CQI, for example.An exemplary reporting sequence is illustrated in FIG. 2, where thenumber in each rectangle corresponds to the report type described above.In one or more embodiments, aperiodic feedback may be requested byFormat 0 downlink control information (DCI) or a random access response(RAR) when a CQI Request bit is set. In one or more embodiments,aperiodic feedback may be transmitted on the PUSCH channel.

Embodiments contemplate that the types of periodic PUCCH feedback may befurther extended for 8 transmit (Tx) antenna ports. Such types ofperiodic PUCCH feedback may include a “Type 1” report that may supportCQI feedback for WTRU selected sub-bands, a “Type 1a” report that maysupport sub-band CQI and second PMI feedback, a “Type 2”, “Type 2b”, and“Type 2c” report that may support wideband CQI and PMI feedback, a “Type2a” report that may support wideband PMI feedback, a “Type 3” reportthat may support RI feedback, a “Type 4” report that may supportwideband CQI, a “Type 5” report that may support RI and wideband PMIfeedback, and a “Type 6” report that supports RI and PTI feedback. CSIfeedback, such as that used in LTE R8 and R10 for example, may bedesigned to support single-cell operation and Physical Downlink SharedChannel (PDSCH) scheduling. The CSI feedback may represent the channelbetween itself and the serving cell and may be reported to the servingcell, and in some embodiments perhaps only to the serving cell.

Embodiments contemplate that or more WTRU feedback procedures may beintended for single cell downlink operation. Embodiments recognize that,for CoMP operation, a WTRU may be required to provide multiple feedbackscontaining CSI information of different CoMP cells or transmissionpoints needed for various functions such as CoMP set determination, CoMPactivation/deactivation, and/or downlink scheduling/beamforming. Severalfeedback configuration embodiments for CoMP implementations arecontemplated. One or more embodiments contemplate addressing bothaspects of content and the rate of the feedback mechanisms.

Embodiments recognize that some feedback procedures defined up to R10may be optimized for the case where some or all transmission points (orantenna ports) of the cell may be geographically close to each other. Indeployments utilizing remote radio heads (RRH), a set of geographicallyseparated RRHs may utilize the same physical cell identity. In thisscenario, using the WTRU to report CSI of some or all deployed antennaports of a same cell using R10 methods may be inefficient because thechannel quality for some antenna ports is likely to be much weaker thanfor other antenna ports. Furthermore, the signals transmitted fromdifferent RRHs may have different characteristics which need to be takeninto account by the WTRU in the evaluation of CSI.

Embodiments contemplate techniques that may allow a WTRU to efficientlyreport the CSI for multiple transmission points. For example,embodiments contemplate techniques that a WTRU may employ to efficientlyreport CSI feedback (e.g., reduces the amount of unnecessary reportingof CSI information). Further, for example, embodiments contemplate howthe WTRU may estimate the CSI for sets of transmission points that maynot be geographically co-located.

Embodiments recognize that CSI may be evaluated and reported assumingthat reference signals are transmitted from a set of closely separatedantennas from a same physical transmission point, and which thereforemay share the same long-term path loss between them and the WTRU. Wherethis assumption may not be satisfied, the CSI may not be useful (oroptimum) to the network for scheduling purposes. For instance, thenetwork may not be able to determine which transmission point or set oftransmission points may be the most appropriate for scheduling the UE ina particular instance.

Embodiments also recognize that the set of transmission points that maybe appropriate for CoMP operation may be dependent on the location ofthe WTRU in the cell. Embodiments contemplate one or more techniques fordetermining appropriate set(s) of transmission points, and/or theassociated sets of reference signals (e.g., CSI-RS) which may beconfigured for the WTRU, for example.

As referred to herein, the phrase “transmission point” may refer to anyantenna port or subset of geographically co-located antenna ports fromthe network that may be transmitting to, or receiving from the WTRU. Theset of transmission points configured or activated for a given WTRU mayor may not belong to the same physical cell identity. A transmissionpoint may transmit one CSI-RS or one set of CSI-RS. Embodimentscontemplate that the phrase “CSI-RS-resource” or “non-zero-powerCSI-RS-resource” may refer to a set of CSI-RS reference signals and/orantenna ports that may be transmitted from one transmission point or oneset of transmission points. In one or more embodiments, characteristicsof these reference signals may be provided to the WTRU by higher layers,such as RRC signaling, for example. A WTRU may be configured with one ormultiple CSI-RS resources for the purpose of CSI evaluation andreporting. The phrase “transmission point” may be used alternativelywith the phrase “CSI-RS resource” where, in one or more embodiments, theCSI-RS-resource may correspond to the transmission point. A transmissionpoint may also transmit at least one common reference signal (CRS) and aWTRU may also measure the at least one CRS for the purpose of CSIevaluation and/or reporting, among other purposes, for example.

Also as referred to herein, a CSI-RS-resource may be a set of CSI-RSreference signals or antenna ports that may be transmitted from onetransmission (or possibly multiple transmission points). Thecharacteristics of these reference signals may be provided to the WTRUby higher layers. The WTRU may be configured with one or multiple CSI-RSresources for the purpose of CSI evaluation and/or reporting, forexample. As described previously, the expression “transmission point”may be substituted by “CSI-RS-resource” where it may be understood thatthe CSI-RS-resource may correspond to the transmission point. Alsoherein, a Per-point rank indication (RI) may correspond to a recommendednumber of useful transmission layers (or rank) for a transmission fromone transmission point. The per-point RI may equivalently be referred toas “per-CSI-RS-resource RI” perhaps if the concerned CSI-RS-resource maybe used for the CSI measurement, or “per-CRS” or “per-cell” RI perhapsif CRS may be used for the CSI measurement.

Further, as referred to herein, per-point CQI may correspond to achannel quality indicator (CQI) that may be applicable to thetransmission of a codeword (or PDSCH transport block) from onetransmission point. The per-point CQI may equivalently be referred to as“per-CSI-RS-resource CQI” perhaps if the concerned CSI-RS-resource maybe used for the CSI measurement, or “per-CRS” or “per-cell” CQI perhapsif a common reference signal (CRS) may be used for the CSI measurement.

As referred to herein, a per-point pre-coding matrix indicator (PMI) ora local precoding matrix indicator may correspond to a recommendedprecoding matrix (or precoder) for a transmission from one transmissionpoint. The per-point PMI may equivalently be referred to as“per-CSI-RS-resource PMI” perhaps if the concerned CSI-RS-resource maybe used for the CSI measurement, or “per-CRS” or “per-cell” PMI perhapsif CRS may be used for the CSI measurement. For the same CSI-RS-resourceor point, embodiments contemplate that there may be more than onepre-coding matrix indicator jointly indicating a single pre-codingmatrix (e.g. a first pre-coding indicator and a second pre-codingindicator, where the latter may vary more rapidly than the former intime).

Also, as referred to herein, joint rank indication or common rankindication may correspond to a recommended number of useful transmissionlayers for a joint transmission from more than one transmission point,which may be corresponding to more than one CSI-RS-resource, forexample.

Aggregated CQI or Joint CQI may correspond to a CQI that may beapplicable to a joint transmission of a codeword from more than onetransmission point, which may be corresponding to more than oneCSI-RS-resource. The aggregated CQI may be estimated assuming a certainpre-coding vector or matrix is used at some or each transmission pointcorresponding to a CSI-RS resource. The aggregated CQI may also beestimated assuming a certain relationship between the precoders used inthe transmission points corresponding to these CSI-RS-resources. Forinstance, it may be assumed that the relative phase between thepre-coders is such that the signals from the transmission points combinecoherently (with a zero phase difference) or combine with apre-determined phase difference, among other contemplated assumptions.

As referred to herein, aggregated PMI or global PMI may correspond to arecommended precoding matrix for a transmission from more than onetransmission point, which may be corresponding to more than oneCSI-RS-resource. The dimensions of the recommended pre-coding matrix maycorrespond to the total number of antenna ports from the at least oneCSI-RS-resource, times the number of layers (or rank), for example.

As referred to herein, inter-point phase indicator or combiningindicator may correspond to a recommended inter-point phase differencefor at least one transmission layer, for at least one pair of precodingmatrices that may be used in transmission points. The inter-point phaseindicator may equivalently be referred to as “inter-CSI-RS-resourceindicator” perhaps if the concerned set of CSI-RS-resources may be usedfor the CSI measurement, or “inter-CRS” or “inter-cell” CQI perhaps if acommon reference signal (CRS) may be used for the CSI measurement.

Also, as referred to herein, the term “CSI of a set of transmissionpoints” may refer to any type of channel state information derived fromany subset of this set of transmission points. For example, it mayinclude channel quality information, rank indication, precoding matrixindications, and/or any type of explicit or implicit feedback. It mayalso include a type of channel state information, heretofore undefined,that is a function of more than one transmission point, as disclosedherein.

Embodiments contemplate devices and techniques, which can be usedindividually or in combination, to efficiently evaluate and/or reportCSI pertaining to transmission points that may be geographicallyseparated. In one or more embodiments, the WTRU may report the CSI ofdifferent transmission points (or CSI-RS-resources), or subsets thereof,that are configured for CSI reporting in different subframes. Thesubsets of transmission points may be determined based on one or moreof: receiving the transmission points (or corresponding referencesignals such as CSI-RS) that are part of each subset from higher layers(e.g., RRC signalling or MAC signalling); and/or one or morecharacteristics of signals received from the transmission points. Forexample, a characteristic of a signal may include, but is not limitedto: the CSI-RS (channel state indicator reference signal) transmittedfrom each Tx point; the CRS (common reference signal) transmitted fromeach point; the physical cell identity used to derive a reference signaltransmitted from some points or each point (e.g., a subset oftransmission points may be defined to correspond to some or alltransmission points from a specific cell; and a quality metric (such asreceived signal strength, received signal quality, and/or channelquality information) of a signal received from each transmission point.

For example, two subsets of transmission points may be defined, whereone may correspond to transmission points received at a relatively highpower level (an “active” subset—for example) for which accurate andtimely CSI information may be required, and the other may correspond totransmission points received at a relatively low level (a “monitored”subset—for example) for which CSI information may not be required, atleast not very frequently. The network could determine whichtransmission points is/are part of each subset and indicate the activeand monitored subsets of Tx points using radio resource controlsignalling. Alternatively, the WTRU could determine whether atransmission point may belong to the active or the monitored group bydetermining whether the received signal strength is above or below athreshold (and in some embodiments, perhaps above or below a thresholdfor a predefined period of time) which could be signalled by the networkthrough higher layers, and/or be function of the received signalstrength of the best transmission point, for example. The configurationof the active set can be done, for example, by providing a set ofnon-zero-power CSI-RS-resources and/or, in some embodiments, a set ofcell identities to the WTRU.

In another example, a first subset of transmission points (the “serving”subset—for example) may be defined as the set of transmission pointsused by the serving cell of the WTRU, while other subsets oftransmission points (“non-serving” subsets—for example) may be definedaccording to the cells from which they are transmitted. In anotherexample, one subset may contain a single specific transmission pointidentified as a “serving” transmission point, while at least one othersubset may contain at least one transmission point identified as“assisting” transmission point. The subframes for which the WTRU reportsCSI of a specific subset of transmission points may be determined by aspecific function of the system frame number and subframe number. Forexample, the function may be defined such that subframes for which atleast a portion of the CSI of a specific subset of transmission pointsis reported may occur periodically. Embodiments recognize that differentportions of the CSI for the same transmission point (e.g. the RI and thePMI/CQI) may use different periodic sets of subframes. The periodicity(and/or offset) may be different for different subsets of transmissionpoints or different types or portions of the CSI. This could allow, forexample, the WTRU to send CSI more frequently for a first subset oftransmission points (the “active” subset or the “serving” subset) thanfor a second subset of transmission points (the “monitored” subset orthe “non-serving” subset). The parameters of the specific functiondetermining in which subframes a specific subset are reported may beprovided by higher layers (e.g. RRC signaling). For instance, higherlayers may provide the periodicity and offset for each subset oftransmission points and/or portions of CSI, perhaps through a singleindex from which these parameters can be derived. Embodiments alsocontemplate the periodicity of a second subset may be determined as apre-determined or signaled multiple of the periodicity of a firstsubset. Also by way of example, one or more embodiments contemplate thatfor certain subsets there may be no periodic reporting at all. For thesesubsets, CSI may be reported if an aperiodic CQI/CSI request is receivedby the WTRU, and in some embodiments perhaps may only be reported if anaperiodic CQI/CSI request is received by the WTRU.

Embodiments contemplate that the type of CSI that may be reported for acertain subset of transmission points may be different than for othersubsets of transmission points. More generally, the CSI reporting modethat may define which part of the CSI is reported in which subframe maybe different for each subset of transmission point. For example, CSIfeedback of a first subset of transmission points can be configured forPUCCH CSI reporting mode 2-1 (where sub-band CQI may be reported) whileCSI feedback of a second subset of transmission points can be configuredfor PUCCH CSI reporting mode 1-1 (where wideband CQI may be reported).In another example, the CSI feedback of a first set of transmissionpoints can be configured for PUSCH reporting mode 2-2 (where sub-bandPMI and CQI may be reported) while CSI feedback of a second subset oftransmission points can be configured for PUSCH reporting mode 1-2(where wideband CQI and sub-band PMI may be reported) or PUSCH reportingmode 3-1 (where wideband PMI and sub-band CQI may be reported).

One or more embodiments contemplate that the WTRU may also report CSI ofa specific subset in a given subframe (n) if it received an aperiodicCSI request in a previous subframe (n-k) where k may be pre-defined orsignaled. Such aperiodic CSI request may, for example, be signaled atthe physical layer by setting a specific field of downlink controlinformation (DCI) to at least one of a subset of values, where the DCImay be signaling an uplink grant and may be transmitted over a PDCCH oranother downlink control channel, such as an enhanced control channel(E-PDCCH). The subset (or set of subsets) for which the WTRU may reportCSI may be determined and/or derived according to one or more of: (1) acharacteristic of the downlink transmission containing the aperiodic CSIrequest; (2) the timing of the subframe where the request is received(n-k) or of the subframe where the CSI is to be reported (n), possiblyexpressed in terms of a system frame number and subframe number; (3) theset of CSI-RS that are received (transmitted) in the same subframe asthe aperiodic CSI request, or the set of CSI-RS that are received ortransmitted in x-y subframe as the aperiodic CSI request, where x is thesubframe in which the aperiodic CSI request is received and y is apredetermined, or configured value; (4) the set of CSI-RS that arereceived (transmitted) in the same subframe as the aperiodic CSIrequest, or the set of CSI-RS that are received or transmitted in x-ysubframe as the aperiodic CSI request, where x is the subframe in whichthe aperiodic CSI request is received and y is a predetermined, orconfigured value; (5) the set of CSI-RS that are received (transmitted)in the same subframe as the aperiodic CSI request, or the set of CSI-RSthat are received or transmitted in x-y subframe as the aperiodic CSIrequest, where x is the subframe in which the aperiodic CSI request isreceived and y is a predetermined, or configured value; (6) acharacteristic of the uplink transmission indicated by the downlinkcontrol signaling that contained the aperiodic CSI request; and/or (7) acombination of the above, such as reserving a codepoint of the aperiodicCSI request field to indicate that the subset of transmission points forwhich CSI is to be reported corresponds to the subset of transmissionpoints used for the transmission of the downlink control signalingindicating the aperiodic CSI request.

In an example, a characteristic of the downlink transmission containingthe aperiodic CSI request may include, but is not limited to: (1) anindication from the downlink control signaling (such as PDCCH)containing the aperiodic CSI request for the UE (e.g., the indicationmay be provided by specific codepoint(s) of an existing field, such asthe CQI request field, or possibly of a field in a heretofore undefinedDCI format); (2) the transmission point(s) used for the transmission ofthe downlink control signaling (such as an evolved PDCCH for example)containing the aperiodic CSI request (e.g., in case downlink controlsignaling is conveyed through an enhanced control channel, the subset oftransmission points for which the WTRU reports CSI could correspond tothe set of transmission points used in the transmission of the enhancedcontrol channel; (3) the cell from which the downlink control signalingcontaining the aperiodic CSI request is transmitted (e.g., the WTRU mayreport the CSI of the subset of transmission points corresponding tothis cell, and in some embodiments the WTRU may only report the CSI ofthe subset of transmission points corresponding to this cell); and/or(4) the subset of cells for which the feedback is to be providedaccording to the value of the CSI request field (e.g. the WTRU mayreport the CSI of the subset of transmission points corresponding tosubset of cells).

One or more embodiments contemplate that the WTRU may report, in a givensubframe, the CSI for a subset of transmission points determinedaccording to one or more of: (1) determining a maximum number M oftransmission points or subsets of transmission points and/or subset ofCSI-RS-resources for which to report CSI. This value may bepre-determined or signaled by higher layers; and/or (2) selecting up toM transmission points or subset thereof, for which the value(s) of anassociated metric are the largest values among all transmission points(or subset thereof) configured for CSI reporting, and/or which may beabove a certain threshold. The associated metric may be representativeof the quality of a signal received from the corresponding transmissionpoint(s) and/or the expected performance of a transmission over thesetransmission points. In one or more embodiments, the metric may beassociated to each transmission point or each subset of transmissionpoints.

Embodiments also contemplate that a single metric may be associated tothe selection of M transmission points. For example, the selection oftransmission points may be based on one or more of: (1) the wideband CQIfrom the transmission point, or the best possible wideband CQI overprecoding matrices for the subset of transmission points; (2) thesub-band CQI if the report is for a particular sub-band, or the maximumof the sub-band CQI over sub-bands, using the best precoding matrix (fora subset of transmission points); (3) the received signal strength(RSRP) from the transmission point(s); (4) the received signal quality(RSRQ) from the transmission point(s); (5) the expected throughput for ahypothetical transmission from the selected transmission points; and/or(6) the maximum rank for a hypothetical transmission from the selectedtransmission points, wherein the same or different layer(s) and/orflow(s) may be received from some transmission points or eachtransmission point.

Embodiments contemplate that the WTRU may choose to select up to Mtransmission points according to one or more of: (1) selecting thetransmission point that provides the best channel quality as measuredby, for example CQI, RSRP, and/or RSRQ, etc. or the like, possiblyassuming at least one precoding matrix; and (2) adding anothertransmission point to the reported set of transmission points if theperformance metric (such as throughput or SINR etc.) is improved by noless than a pre-defined threshold, and in some embodiments perhaps onlyif the performance metric (such as throughput or SINR etc.) is improvedby no less than a pre-defined threshold. In one or more embodiments, themetric associated to the selection of M transmission points as describedherein may persist for a predefined period of time. For example, if themetric relies on the CQI report, a transmission point may be selected ifthe measured quantity is above/below a threshold for a period of time.

Embodiments contemplate that an activation state may be defined fortransmission point(s) or subset(s) thereof. In a given subframe, theWTRU may report the CSI for transmission point(s) and/or subset(s)thereof, which are in the “active” state. In one or more embodiments,the WTRU may not measure quality of reference signal(s) associated tonon-active transmission point(s) or subset(s) thereof. The activationstate may be determined using one or more of: (1) setting the initialactivation state following configuration of transmission point(s) orsubset(s) thereof to either “active” or “non-active”; and/or (2)explicit activation or de-activation through reception an activation orde-activation command. The command may be conveyed by, for example,physical layer signaling such as from the reception of a PDCCH controlsignaling (e.g., a DCI) with one or more of the followingcharacteristics: the DCI is scrambled using a Radio-Network Identifier(RNTI) which may indicate the use of at least one CoMP function; the DCIindicates at least one radio resource assignment (e.g. a downlinkassignment) such that said assignment indicates that CoMP is applicablefor the transmission; and/or any of the above characteristic where saidsignaling may include an indication (e.g. a bit) for activation and/ordeactivation of at least one CoMP function. Further, the command may beconveyed by one or both of MAC layer signaling (e.g. MAC controlelement); and/or RRC signaling. Embodiments contemplate that implicitde-activation may occur when one or more conditions are detected, suchas, for example: a metric associated to the transmission point, orsubset thereof, falls below a threshold; the WTRU reports one or moremeasurements that may trigger the network to start utilizing thetransmission point, or subset thereof, for transmission to the WTRU;and/or a timer that was started (or re-started) at the last transmissionfrom the network utilizing the transmission point(s), or subset thereof,expires.

For one or more of the signaling methods described previously, one ormore embodiments contemplate that the WTRU may transmit a HARQ A/N toacknowledge the activation/deactivation of the CoMP function. Inaddition, the signaling procedure may be built based on an index table,(e.g. 00, 01, 10, 11) to a configuration of the CSI reporting/modeand/or reporting CoMP Set, and/or feedback format, and/or feedbackresource to use, for example.

Embodiments contemplate techniques that may be used to indicate a set oftransmission points in the uplink for the purpose of CSI reporting ormeasurement reporting, and/or in downlink control signaling (such as aDCI format of a PDCCH or enhanced PDCCH) for the purpose of aperiodicCSI request or data transmission. For example, the WTRU may indicate (ormay have indicated to it) the transmission point(s) or subset(s) oftransmission points by a bitmap where each bit position may correspondto a specific transmission point or subset thereof. In another example,the subset of transmission point(s) may implicitly be indicated by acharacteristic of transmission of the concerned signaling, such as, thetiming of the subframe of the transmission of the concerned signaling(CQI report, DCI, etc.), and the transmission points used for thetransmission of the concerned signaling. In another example, apre-defined sequence of bits may be used to replace the CSI oftransmissions points for which CSI is not reported. In another example,an index may be associated with some or each CSI-RS-resource in theconfiguration. The WTRU may report this index together with theassociated CSI report. The index may be explicitly provided orimplicitly determined in the WTRU according to the order of the receivedconfigurations in the RRC message, for example.

Embodiments contemplate components of the CSI feedback of a set of Ktransmission points. The measurements that may be used as a basis forthe determination of CSI feedback may be derived from at least one of aset of following signals: CSI-RS reference signals; CRS referencesignals; and/or other types of reference signals. Such reference signalsmay be transmitted on a number A_(k) of (reference signal) antenna portsfor the kth transmission point of the set. The configuration of antennaports for some or each transmission point, as well as one or moremapping techniques for the associated reference signals, arecontemplated by embodiments.

One or more embodiments contemplate that the WTRU may report a “JointRank indication” RI_(joint) or “Common rank indication” that may beachieved for a joint transmission over some or all K transmission pointsof the set. The Joint Rank Indication may be interpreted, for example,as the recommended number of useful transmission layers (or rank) forjoint transmission over the K transmission points. The WTRU may report aper-point rank indication RI_(k) which may correspond to the recommendednumber of useful transmission layers (or rank) for transmission over thek^(th) transmission point, and in some embodiments perhaps over thek^(th) transmission point only. The per-point rank indication may alsobe referred to as “per-CSI-RS-resource rank indication” in case a CSIevaluation is based on CSI-RS measurement, for example.

Embodiments contemplate that per-point rank indication may includeunconditioned per-point rank indication and/or conditioned per-pointrank indication. Unconditioned per-point rank indication RI_(k) mayindicate a transmission to the WTRU (and in some embodiments perhaps tothe WTRU only) over transmission point k, without any assumption on theprecoding utilized on other transmission points for other WTRU(s).Conditioned per-point rank indication RI_(k) may indicate a transmissionto the WTRU (and in some embodiments perhaps to the WTRU only) overtransmission point k, assuming that transmission to other WTRU's takesplace on other transmission points with one or more precoders. The oneor more precoder(s) may be indicated by the WTRU for the othertransmission points, whose use may result in maximum interference to theWTRU. Alternatively or additionally, in one or more embodiments, the oneor more precoder(s) may be indicated by the WTRU for the othertransmission points, whose use may result in minimum interference to theWTRU. The one or more precoder(s) may include a “zero” precoder (e.g.,no transmission or “muting”). Precoders from the subset of precoders maybe indicated by the WTRU for the other transmission points, such as froma set of allowed precoders, or from outside a set of restrictedprecoders. The use of such precoders may allow the WTRU to properlyreceive data from relevant transmission points. The WTRU may receivedata from relevant transmission points independently. The rankindication(s) may be reported for the whole frequency band or for aspecific set of sub-bands, for example.

In one or more embodiments, a WTRU may report at least one channelquality index (CQI) corresponding to at least one combination oftransmission parameters (e.g., modulation, code rate, transport blocksize). By way of example, this combination may be such that a singlePDSCH transport block (e.g., codeword) occupying a certain CSI referenceresource can be received with a transport block error probability notexceeding a pre-determined threshold (such as 0.1, for example).Different types of CQI may be defined based on the assumed type oftransmission over the K transmission points, as described herein.

Embodiments contemplate that CQI may include several types, such as“joint CQI” or “aggregated CQI” (CQI_(joint)) and “per-point CQI” or“per-CSI-RS-resource CQI” (CQI_(k)). Joint (or aggregated) CQI(CQI_(joint)) may include the CQI for a joint transmission of a codewordover some or all K transmission points of the set. When the WTRU usesjoint CQI, assumptions may be made on the transmission state or CSIprocess of the points in the set for which CQI is being fed back. Forexample, a point may be in one of the following states: transmitting tothe WTRU, interfering to the WTRU (e.g., transmitting to another WTRU),muted (e.g., blanked), or unknown. Unknown state(s) may indicate thatthe WTRU makes no assumption on the transmission state or CSI process ofthe point, and the point may be in one of the three aforementioneddefined states. The points that are assumed to be transmitting to theWTRU may transmit coherently or non-coherently. The WTRU may feedbackcoherent joint (or aggregated) CQI and non-coherent joint (oraggregated) CQI, based on the assumption made on the transmittingpoints. Joint (or aggregated) CQI may include coherent joint CQI andnon-coherent joint CQI. Coherent joint (or aggregated) CQI may assumethat symbols of a codeword may be transmitted over up to K transmissionpoints using a determined relationship between the precoders used ineach K transmission points, possibly according to a combining matrix orcombining indicator, described herein. For instance, it may be assumedthat the relative phase between the pre-coders is such that the signalsfrom the transmission points combine coherently (with a zero phasedifference) or combine with a pre-determined phase difference.Non-coherent joint (or aggregated) CQI may assume that symbols of acodeword may be transmitted over up to K transmission points, without adetermined relationship between the precoders used in some or each Ktransmission points.

Embodiments contemplate evaluating CQI for a transmission from more thanone transmission point, for example. In one or more embodiments, a WTRUmay estimate the received signal strength S_(RS,i) of at least oneresource element in which it is known that a CSI-RS or CRS signal ispresent according to the WTRU configuration. A ratio P_(c,i) may bedetermined between the energy per resource element (EPRE) of thisreference signal (CSI-RS or CRS) and the EPRE of the PDSCH transmissionfor the at least one resource element. The WTRU may evaluate asignal-to-interference ratio (SIR) for a hypothetical PDSCH transmissionas the ratio between the signal strength of the PDSCH transmissionS_(PDSCH) and the interference I, where S_(PDSCH) may be determined as afunction of at least one (S_(RS,i)/P_(c,i)) term, such as for instanceS_(PDSCH)=Sum_over_i (S_(RS,i)/P_(c,i)). The interference I may beestimated by measuring energy from other resource elements provided bythe network, among other techniques, for example.

Per-point CQI or per-CSI-RS-resource CQI (CQI_(k)) may include the CQIfor a transmission of a codeword to this WTRU over the k^(th)transmission point, and in some embodiments perhaps only over the k^(th)transmission point. Per-point CQI may include unconditioned per-pointCQI_(k) and conditioned per-point CQI_(k). Unconditioned per-pointCQI_(k) may indicate CQI for a transmission of a codeword to this WTRUover transmission point k (and perhaps only over transmission point k),without any assumption on the precoding utilized on other transmissionpoints for other WTRU's, or for independent data to the WTRU.Conditioned per-point CQI_(k) may indicate CQI for a transmission of acodeword to this WTRU over transmission point k (and perhaps only overtransmission point k), assuming that transmission to other WTRU's takesplace on other transmission points with one or more precoder(s). Theprecoder(s) may be indicated by the WTRU for the other transmissionpoints, which use may result in maximum interference to the WTRU. Theprecoder(s) may be indicated by the WTRU for the other transmissionpoints, which may result in minimum interference to the WTRU. Theprecoder(s) may include a “zero” precoder (e.g., no transmission or“muting”). Precoders from the subset of precoders may be indicated bythe WTRU for the other transmission points, such as from a set ofallowed precoders, or from outside a set of restricted precoders, forexample. The use of such precoders may allow the WTRU to properlyreceive data from relevant transmission points. The CQI may be reportedfor the whole frequency band or for a specific set of sub-bands, forexample.

In case more than one of the above types/sub-types of CQI are reportedfor at least one codeword, the WTRU may report, for a firsttype/sub-type of CQI applicable to a first codeword, the differencebetween the value of this first type/sub-type of CQI and the value of asecond type/sub-type of CQI applicable to the same codeword or a secondcodeword. For instance, the second type/sub-type of CQI for a codewordmay be encoded differentially with respect to the respective firsttype/sub-type of CQI.

One or more embodiments contemplate that a WTRU may report at least oneprecoding matrix indicator (PMI) applicable to a set of K transmissionpoints. PMI may include global precoding matrix indicator, localprecoding matrix indicator, and interference precoding matrix indicator.

At least one global precoding matrix indicator may correspond to aglobal (or “aggregated”) precoding matrix W of dimension (A₁+A₂+ . . .A_(K))×RI_(joint). This matrix may represent a recommended precoder forthe transmission of data for this WTRU over some or each of RI_(joint)layers from some or all K transmission points. In one or moreembodiments, the interpretation of the global (or aggregated) PMI maydepend on the last reported joint rank indication RI_(joint).

A local (or “per-point” or “per-CSI-RS-resource”) precoding matrixindicator for a transmission point k may include a matrix W_(k) ofdimension A_(k)×RI_(k). This matrix may represent a recommended precoderfor the transmission of data for this WTRU over each of RI_(k) layersfrom the k^(th) transmission point. The interpretation of the local (orper-point) PMI may depend on the last reported per-point rank indicatorRI_(k).

A precoding matrix indicator for a transmission point k may include amatrix Y_(k). This matrix represents a precoder that may be used fortransmission of undesired data, such as data transmitted for anotherWTRU from the k^(th) transmission point. This precoder may correspond toat least one of a precoder for transmission to at least one other WTRU,which may result in minimum interference to the WTRU for at least onetransmission layer. It may also correspond to a precoder fortransmission to at least one other WTRU, which may result in maximuminterference to the WTRU for at least one transmission layer.

Embodiments contemplate that a set of precoding matrices W for one ormore transmission points k₁ may correspond to a set of precoders. Theset of precoding matrices may include groups of precoder matrices. Theset may correspond to a set of precoder(s) that may not be used by thetransmission point k₁ to ensure the WTRU may correctly receive, possiblyindependent, data from other transmission point(s) (e.g., k₂). The setmay correspond to a set of precoder(s) from which the transmission pointk₁ may select a precoder in the event the transmission point k1 choosesto not use the precoder identified by the precoder matrix indication fedback by the WTRU.

Embodiments contemplate that the at least one precoding matrix indicatorcorresponding to a local (or per-point) precoding matrix W_(k) mayinclude one or more of:

-   -   A single index i_(k) which corresponds to a precoding matrix        W_(k) according to a pre-defined mapping, and which        interpretation may depend on the last reported per-point rank        indication RI_(k); or    -   One or two indices i_(1k) and/or i_(2k) which correspond to a        precoding matrix W_(k) according to a pre-defined mapping, which        may depend on the last reported per-point rank indication        RI_(k). A first index i_(1k) may correspond to a property of the        precoding matrix that may not change on a short-term basis, for        example, at least one set of weights (or beams) applied to at        least one group of antenna ports, where the at least one group        of antenna ports may depend on the per-point rank indication        RI_(k). A second index i_(2k) may correspond to a property of        the precoding matrix that may change on a short-term basis, for        example, for each of the RI_(k) transmission layers, the        selected beam from each of the groups of antenna ports and        combining information (e.g. co-phasing) between these beams.        Embodiments contemplate that whether a single index or two        indices are reported for this transmission may depend on:        higher-layer signaling or configuration; and/or number of        antennas in the transmission point.

Embodiments contemplate that the one or more precoding matrix indicatorscorresponding to the global precoding matrix W may include one or moreof the following:

-   -   For each transmission point k, at least one per-point precoding        matrix indicator corresponding to a local precoding matrix W_(k)        (e.g., i_(k), or a pair i_(1k), i_(2k)) as described previously.    -   At least one combining indicator i_(comb), (or inter-point        indicator, or inter-CSI-RS-resource indicator) which may        correspond to a combining matrix W_(comb) of dimension (RI₁+RI₂+        . . . +RI_(K))×RI_(joint), and which interpretation may depend        on the last reported joint rank indication RI_(joint) and        possibly set of per-point rank indications RI_(k). The combining        matrix W_(comb) indicates, for each of the RI_(joint)        transmission layers of the combined set of transmission points,        which beam (if any) of the last reported local precoder of each        transmission point is used, and co-phasing information between        the beams of these transmission points. The indicator may also        provide relative amplitude information, for example.        The global precoding matrix W corresponding to this set of        precoding matrix indicators may then be obtained with the        following exemplary formula (where rows are separated by        semicolons):

W=[W ₁0 . . . 0;0W ₂0 . . . 0;00W _(k). . . 0; . . . ;0 . . . 0W _(K)]×W_(comb)

Embodiments contemplate that the one or more combining indicatorsi_(comb) may include one or more of:

-   -   At least one index to a specific combining matrix W_(comb)        according to a pre-defined mapping;    -   An indication of whether the global (or aggregated) precoding        matrix is such that each layer is transmitted over at most one        transmission point (i.e. whether the matrix W_(comb) is the        identity matrix);    -   At least one indication of the phase difference (or correction)        that should be applied, for each transmission layer, to or        between the local (or per-point) precoders of each transmission        point. In more or more embodiments, the phase difference for a        specific “reference” per-point pre-coder may be fixed to zero;        in this case, the phase difference may be referred to as        “inter-point phase information”.

By way of example, and not limitation, embodiments contemplate: oneindication for each transmission point of a quantized timing offset &cfor at least one transmission layer, where the reference may be thetiming of one specific transmission point; one indication for eachtransmission point (i_(k,comb)) of the phase difference (or correction)that should be applied, for each transmission layer, to the precoders ofthis transmission point for coherent combining; and/or two indicationsfor each transmission point (i_(1k,comb) and i_(2k,comb)) of the phasedifference (or correction) that may be applied, for each transmissionlayer, to the precoders of this transmission point for coherentcombining, where

-   -   One per-point indication i_(1k,comb) may correspond to a        property of the phase correction that does not change on a        short-term basis, such as the M most significant bits of a        quantized phase correction; and/or    -   One per-point indication i_(2k,comb) may correspond to a        property of the phase correction that may change on a short-term        basis, such as the L least significant bits of a quantized phase        correction.

Embodiments contemplate that one or more precoding matrix indicatorscorresponding to the global (or aggregated) precoding matrix W may alsoinclude the following:

-   -   For each transmission point k, an index i_(1k) which corresponds        to a property of the global (or aggregated) precoding matrix        that may not change on a short-term basis, for example, at least        one set of weights (or beams) applied to at least one group of        antenna ports from transmission point k, where the at least one        group of antenna ports may depend on a per-point rank indication        RI_(k) or on a joint (or common) rank indication RI_(joint);    -   The set of i_(1k) indices may be concatenated into a single        joint (or aggregated) long-term precoding index i_(1joint);        and/or    -   An index i_(2comb) which may correspond to a property of the        global precoding matrix W that may change on a short-term basis,        for example, for each of the RI_(joint) transmission layers, the        selected beam from some or each of the groups of antenna ports        from some or all transmission points and combining information        (e.g. co-phasing) between these beams.

Embodiments contemplate that a global (or aggregated) precoding matrix Wmay include a single index i₁ (and perhaps a single index i₁) that maycorrespond to a property of the global precoding matrix, which may notchange on a short-term basis. For example, index i₁ may correspond to aset of weights and/or beams that may be applied to the transmissionpoints. The global (or aggregated) precoding matrix W may include anindex i_(2k) for each transmission point k. Index i_(2k) may correspondto a property of each local (or per-point) precoding matrix that maychange on a short-term basis. For example, index i_(2k) may correspondto the selected subset of weights and the co-phasing between eachpolarization for each of the RI transmission layers.

For example, if a WTRU may receive one layer from two transmissionpoints, each with 4 x-pol transmit antennas, signal y=Wx+z may bereceived, where y may be the n_(r)×1 vector of received signals, x maybe the n₁×1 vector of transmitted signals (with n₁=1), z may be then_(r)×1 noise vector, and W may be the n_(r)×n₁ precoding matrix. Thefour ports assigned to transmission point ‘a’ may be represented asa₁,a₂,a₃,a₄, and the four ports of transmission point ‘b’ may berepresented as b₁,b₂,b₃,b₄. The precoding matrix may be mapped to theantenna ports as follows: W→[a₁, a₂, b₁, b₂, a₃, a₄, b₃, b₄]T. Thefollowing codebook structure could be used (see also Table 2):

$\varphi_{n_{k}} = \begin{bmatrix}e^{j\pi{n_{k}/2}} & 0 \\0 & e^{j\pi{n_{k}/2}}\end{bmatrix}$ $\varphi_{n_{1},n_{2}} = \begin{bmatrix}\varphi_{n_{1}} & 0 \\0 & \varphi_{n_{2}}\end{bmatrix}$ $v_{m} = \begin{bmatrix}1 & e^{{j2}\;\pi\;{n/32}} & e^{j\; 4\pi\;{n/32}} & e^{j\; 6\;\pi\;{n/32}}\end{bmatrix}^{T}$

TABLE 2 Exemplary Codebook for 1-layer CSI reporting i_(2a) i₁ 0 1 2 3 45 6 7 0-15 W_(2i) ₁ _(,0,i) _(2b) ⁽¹⁾ W_(2i) ₁ _(,1,i) _(2b) ⁽¹⁾ W_(2i)₁ _(,2,i) _(2b) ⁽¹⁾ W_(2i) ₁ _(,3,i) _(2b) ⁽¹⁾ W_(2i) ₁ _(+1,0,i) _(2b)⁽¹⁾ W_(2i) ₁ _(+1,1,i) _(2b) ⁽¹⁾ W_(2i) ₁ _(+1,2,i) _(2b) ⁽¹⁾ W_(2i) ₁_(+1,3,i) _(2b) ⁽¹⁾ i_(2a) i₁ 8 9 10 11 12 13 14 15 0-15 W_(2i) ₁_(+2,0,i) _(2b) ⁽¹⁾ W_(2i) ₁ _(+2,1,i) _(2b) ⁽¹⁾ W_(2i) ₁ _(+2,2,i)_(2b) ⁽¹⁾ W_(2i) ₁ _(+2,3,i) _(2b) ⁽¹⁾ W_(2i) ₁ _(+3,0,i) _(2b) ⁽¹⁾W_(2i) ₁ _(+3,1,i) _(2b) ⁽¹⁾ W_(2i) ₁ _(+3,2,i) _(2b) ⁽¹⁾ W_(2i) ₁_(+3,3,i) _(2b) ⁽¹⁾${{where}\mspace{14mu} W_{m,n_{1},n_{2}}^{(1)}} = {\frac{1}{\sqrt{8}}\begin{bmatrix}v_{m} \\{\varphi_{n_{1},n_{2}}v_{m}}\end{bmatrix}}$

The same long-term/wideband PMI i₁ may be used by both transmissionpoints. Each transmission point may have its own short-term/narrowbandi₂ (such as i_(2a) and i_(2b)). Index i₁ may require 4 bits of feedback,while index i_(2a) may require 4 bits and index i_(2b) may require 2bits. For example, precoding at transmission point a may require i₁ andi_(2a). Precoding at transmission point b may require i₁, i_(2a) andi_(2b). An alternative transmission point b may, for example, only havefeedback i₁ and i_(2b). To remove the dependence on i_(2a) attransmission point b, the codebooks at each transmission point mayinclude (see Tables 3 and 4):

TABLE 3 Exemplary Codebook for 1-layer CSI reporting at transmissionpoint a. i_(2a) i₁ 0 1 2 3 4 5 6 7 0-15 W_(2i) ₁ _(,0) ⁽¹⁾ W_(2i) ₁_(,1) ⁽¹⁾ W_(2i) ₁ _(,2) ⁽¹⁾ W_(2i) ₁ _(,3) ⁽¹⁾ W_(2i) ₁ _(+1,0) ⁽¹⁾W_(2i) ₁ _(+1,1) ⁽¹⁾ W_(2i) ₁ _(+1,2) ⁽¹⁾ W_(2i) ₁ _(+1,3) ⁽¹⁾ i_(2a) i₁8 9 10 11 12 13 14 15 0-15 W_(2i) ₁ _(+2,0) ⁽¹⁾ W_(2i) ₁ _(+2,1) ⁽¹⁾W_(2i) ₁ _(+2,2) ⁽¹⁾ W_(2i) ₁ _(+2,3) ⁽¹⁾ W_(2i) ₁ _(+3,0) ⁽¹⁾ W_(2i) ₁_(+3,1) ⁽¹⁾ W_(2i) ₁ _(+3,2) ⁽¹⁾ W_(2i) ₁ _(+3,3) ⁽¹⁾${{where}\mspace{14mu} W_{m,n_{1}}^{{(1)}a}} = {{{\frac{1}{\sqrt{8}}\begin{bmatrix}v_{m}^{a} \\{\varphi_{n_{1}}v_{m}^{a}}\end{bmatrix}}\mspace{14mu}{and}\mspace{14mu} v_{m}^{a}} = \left\lbrack \begin{matrix}v_{m,1} & \left. v_{m,2} \right\rbrack^{T}\end{matrix} \right.}$

TABLE 4 Exemplary Codebook for 1-layer CSI reporting at transmissionpoint b. i_(2b) i₁ 0 1 2 3 4 5 6 7 0-15 W_(2i) ₁ _(,0) ⁽¹⁾ W_(2i) ₁_(,1) ⁽¹⁾ W_(2i) ₁ _(,2) ⁽¹⁾ W_(2i) ₁ _(,3) ⁽¹⁾ W_(2i) ₁ _(+1,0) ⁽¹⁾W_(2i) ₁ _(+1,1) ⁽¹⁾ W_(2i) ₁ _(+1,2) ⁽¹⁾ W_(2i) ₁ _(+1,3) ⁽¹⁾ i_(2b) i₁8 9 10 11 12 13 14 15 0-15 W_(2i) ₁ _(+2,0) ⁽¹⁾ W_(2i) ₁ _(+2,1) ⁽¹⁾W_(2i) ₁ _(+2,2) ⁽¹⁾ W_(2i) ₁ _(+2,3) ⁽¹⁾ W_(2i) ₁ _(+3,0) ⁽¹⁾ W_(2i) ₁_(+3,1) ⁽¹⁾ W_(2i) ₁ _(+3,2) ⁽¹⁾ W_(2i) ₁ _(+3,3) ⁽¹⁾${{where}\mspace{14mu} W_{m,n_{2}}^{{(1)}b}} = {{{\frac{1}{\sqrt{8}}\begin{bmatrix}v_{m}^{b} \\{\varphi_{n_{2}}v_{m}^{b}}\end{bmatrix}}\mspace{14mu}{and}\mspace{14mu} v_{m}^{b}} = \left\lbrack \begin{matrix}v_{m,3} & \left. v_{m,4} \right\rbrack^{T}\end{matrix} \right.}$In this case, some transmission points or each transmission point mayreceive i₁ (4 bits) as well as their respective i₂ (each 4 bits), forexample.

The set of precoding matrices W_(k)′ may include an index (and perhaps asingle index) that may correspond to a group of precoding matricesaccording to a predetermined mapping. The interpretation of the group ofprecoding matrices may depend on the last reported per-point rankindication RI_(k) and/or the precoding matrix indicator that correspondsto the desired precoding matrix to be used for this WTRU. The set ofprecoding matrices may include multiple indices, each indicatingspecific precoding matrices according to a predetermined mapping whosegrouping constitutes the set, for example.

In one or more embodiments, a WTRU may report at least one poweradjustment indicator PAI_(k) for at least one transmission point. Thepower adjustment indicator PAI_(k) may maps to a value of a recommendedpower adjustment for at least one of the DM-RS reference signal and thedata symbols for a transmission to this WTRU from transmission point k.This may allow the network to better balance received power from some orall transmission points. The mapping between the power adjustmentindicator and the actual power adjustment (e.g. in dB) may bepre-defined or provided by higher layers, for example. In one or moreembodiments, the WTRU may report channel state information assuming acertain type of single-point or multi-point transmission from thenetwork. Such transmission hypotheses can be referred to as a“transmission state” or “CSI processes” herein. The transmission stateor CSI process may include, for at least one transmission point, anassumption about whether this transmission point is:

-   -   Transmitting to the WTRU according to the reported per-point or        aggregated precoding matrix indicator;    -   Transmitting to another WTRU according to the reported per-point        or aggregated precoding matrix indicator; and/or    -   Not transmitting to any WTRU (for example, muted or blanked).        In one or more embodiments, for a given transmission state or        CSI process, there may not be any assumption made for at least        one transmission point.

In one or more embodiments, the reporting of CSI for a certaintransmission state or CSI process may be configured by higher layersusing different methods. Such CSI processes may be referred to as “CSIcase”, “CSI type”, and/or “CSI hypothesis” as described herein. In oneor more embodiments, one or more reporting modes may be configured forone or more, or each, of the CSI processes. In one or more embodiments,one or more periodic and/or aperiodic reports and/or report types (e.g.,a rank indicator (RI)) may correspond to the one or more reporting modesand/or the one or more CSI processes.

For example, one or more embodiments contemplate that the WTRU may beconfigured to report a certain CSI case or CSI process by beingindicated at least one CSI-RS resource corresponding to point(s) fromwhich the desired signal may be assumed to be transmitted and/or atleast one CSI-RS resource corresponding to point(s) from which aninterfering signal may be assumed to be transmitted according to thetransmission state or CSI process. In addition, the WTRU may also beconfigured with an interference measurement resource or CSI-IM, whichmay include a set of resource elements in certain subframes (such as aset of resource elements corresponding to at least one zero-power CSI-RSresource) in which to measure the noise and interference generated bytransmissions from other points in the network, for example.

Alternatively or additionally, one or more embodiments contemplate thatthe WTRU may be configured to report a certain CSI case or CSI processby being indicated at least one CSI-RS resource corresponding topoint(s) from which the desired signal may be assumed to be transmitted,and/or at least one interference measurement resource which includes aset of resource elements in certain subframes in which to measure thenoise and interference, perhaps including interference generatedaccording to the transmission state or CSI process, for example.

In one or more embodiments, a specific CSI case or CSI process may beassociated to a certain serving cell or a certain carrier frequency,perhaps in case the WTRU may be configured with multiple serving cells(carrier aggregation), for example.

The transmission point may be in a transmission state or CSI processsuch as (T)ransmitting, (I)nterfering (e.g. undesired transmission, forexample, to another WTRU), (B)lanked and/or (U)nknown. For example, forn points, there may be up to 4^(n) possible Transmission State Vectors(TSV). Some or each Transmission State Vector may be indicated by one ormore Transmission State Indicator (TSI). The TSI may be a scalar valuethat may map to the TSV or may be the TSV itself. Additionally oralternatively, the TSI may be a bitmap representing the TSV. Also by wayof example, the WTRU may feedback with assumptions on five points thatmay include two transmitting points, two interfering points and oneblanked/muted point. An exemplary corresponding TSI may include a vectorsuch as [T T I I B]. The exemplary corresponding TSI may include a valuethat may map to a vector such as [T T I I B]. Additional transmissionstates or TSI or CSI processes may be defined to indicate whether ajoint transmission may be assumed to be coherent (e.g., use combiningindicator or inter-point phase information) or non-coherent.

Embodiments contemplate that a WTRU may be configured to report CSI forcertain possible transmission states or CSI processes, and in someembodiments perhaps for only certain possible transmission states or CSIprocesses. For instance, the WTRU may be configured to report CSI for 2points and may be configured to report CSI for the followingtransmission states or CSI processes:

-   -   Single transmission from the first point, with the second point        transmitting to another WTRU (or, using the previous        terminology, [T I], for example);    -   Single transmission from the first point, with the second point        not transmitting to any WTRU (or, using above terminology, [T        B], for example);    -   Single transmission from the second point, with the first point        transmitting to another WTRU (or, using above terminology, [I        T], for example);    -   Single transmission from the second point, with the first point        not transmitting to any WTRU (or, using above terminology, [B        T], for example); and/or    -   Joint transmission from both points (or, using the above        terminology, [T T], for example).        Embodiments contemplate that the set of transmission states, or        CSI processes, and/or set(s) of TSV for which the WTRU may        potentially report CSI can be configured by higher layers. Some        transmission states or CSI processes or each transmission state        or CSI process for which the WTRU may potentially report CSI may        be indicated by an index or “CSI index”. For instance, the CSI        index may correspond to the order in which the different CSI        cases are being configured by higher layers.

Embodiments contemplate that transmission state or CSI process selectionmay be controlled by the network. The network may determine thetransmission state or CSI process or TSI value(s) (e.g. TSI value(s)corresponding to a CSI report), or CSI case. The network may indicate aTSI and/or TSV for the WTRU to use via higher layer signaling. Thenetwork may indicate a TSI and/or TSV for the WTRU to use for periodicor aperiodic feedback grant, for example. The TSI may be used for oneinstance of aperiodic feedback, or may be used for the duration of asemi-persistent aperiodic feedback grant. In one or more embodiments,the TSI may be associated with one or more subframe number(s). Theassociation may be preconfigured by higher layer signaling. In one ormore embodiments, the TSI and/or TSV may be based on a previousfeedback. For example, the WTRU may feedback an indicator that mayindicate to the network that the TSI and/or TSV has changed. The new TSIand/or TSV may cycle to another preconfigured value. For example, theWTRU may feedback an indicator that may indicate to the network that theTSI and/or TSV should be changed. The network may be prompted toindicate the new TSI and/or TSV to the WTRU before another CSI feedbackis performed by the WTRU.

In one or more embodiments, the TSI (or CSI case) may depend on thetiming of the reception of CSI-RS resources compared to the timing ofthe CSI report transmission (or of the aperiodic CSI request). Forinstance, the WTRU may report the CSI case(s) tied to a subset of CSI-RSresources received in the latest subframe satisfying:

-   -   At least one CSI-RS resource is transmitted in the subframe        according to the configuration; and/or    -   The timing of the subframe is at least k subframes before the        subframe in which CSI is reported (or alternatively in which        aperiodic CSI is requested)        In the aforementioned CSI cases may be CSI cases which use the        aforementioned CSI-RS resources(s) as an assumed desired signal.        Alternatively or additionally, it may be the CSI case(s) which        use the CSI-RS resource(s) as an assumed interfering signal, or        as interference measurement resource. This selection criterion        may apply to subframes in which more than a maximum number of        periodic CSI reports are configured to be transmitted (and in        some embodiments perhaps only to such subframes) and/or for        which a prioritization according to CSI case or CSI process may        apply (and in some embodiments perhaps must apply).

In one or more embodiments, TSI/TSV selection may be controlled by theWTRU. For example, the WTRU may feedback the TSI and/or TSV to informthe network of the conditions with which the CSI feedbacks have beencalculated. The WTRU may determine the TSI and/or TSV value(s). Forexample, for n points, the WTRU may select from the 4^(n) possible TSIand/or TSV values. For example, the WTRU may select from a subset ofpossible TSI and/or TSV values. The subset of possible TSI and/or TSVvalues may be signaled to the WTRU. For example, the subset may besignaled to the WTRU by one or more methods described above with respectto network-controlled TSI and/or TSV selection (e.g., by replacing TSIwith TSI set). For example, the subset of possible values may includethe TSVs with a single point (T)ransmitting. In some embodiments, noother condition on other points may be used (e.g., DPS without muting).For example, the subset of possible values may include the TSIs with atleast two points (T)ransmitting and other points (B)lanked (e.g.,joint-transmission with blanking). The WTRU may feedback an indicator tothe network indicating that the selected TSI and/or TSV has changed. Thenew TSI and/or TSV may be pre-configured, or may be fed back by theWTRU, for example.

As described above, the WTRU may select TSI(s) and/or TSV(s) from a setof possible transmission states or CSI processes or a set of possiblevalues (e.g. including in an embodiment a subset of the possible 4^(n)values, where n is the number of points). The TSI and/or TSV may beselected based on the number of points required to achieve apre-configured threshold on performance. For example, the WTRU mayselect the TSI(s) and/or TSV(s) that may require the fewest (or most)points to transmit to achieve a pre-configured threshold on performance(for example, maximizing the SINR, minimizing the BLER, maximizing thethroughput, or the like). The TSI(s) and/or TSV(s) may be selected basedon the number of points that may need to be blanked to achieve apre-configured threshold on performance. For example, the WTRU mayselect the TSI(s) and/or TSV(s) that may require the fewest (or most)points to be blanked to achieve a pre-configured threshold onperformance (for example, maximizing the SINR, minimizing the BLER,maximizing the throughput, or the like). For example, select the CSIcase or CSI process which may be associated to a certain number ofCSI-RS resources from which an interfering signal may be assumed to betransmitted (e.g., where the number may be 0, or a positive number).

The TSI(s) and/or TSV(s) may be selected based on the restrictions onnon-transmitting points. For example, the WTRU may select the TSI(s)and/or TSV(s) that may impose the fewest (or most) restrictions onnon-transmitting points (the fewest (or most) unknown points) to achievea pre-configured threshold on performance (for example, maximizing theSINR, minimizing the BLER, maximizing the throughput, or the like). Inone or more embodiments, the TSI(s) and/or TSV(s) may be selected basedon CQI and/or rank (e.g. (RI)). For example, the WTRU may select theTSI(s) and/or TSV(s) that may have the highest CQI and/or the highestrank (e.g. (RI)).

Additionally or alternatively, the TSI(s) and/or TSV(s) may be selectedbased on throughput or an amount of bits that may be transferred. Forexample, the WTRU may select the TSI(s) and/or TSV(s) that may maximizethe total throughput or the total amount of bit that may be transferredin a subframe if the network followed a recommended CSI (e.g. includingboth CQI and RI). In one or more embodiments, the WTRU may select a TSIand/or TSV from the allowed TSI and/or TSV subset. The allowed TSIand/or TSV subset may include TSIs and/or TSV(s) that correspond topoints that are in the (T)ransmitting state and satisfy one or more ofthe following criteria: surpass a minimal allowable path loss threshold,achieve a minimal per-point CQI threshold, and/or surpass a certainper-point CQI differential threshold when compared to the maximumper-point CQI threshold.

Embodiments contemplate that in evaluating CSI for a transmission stateor CSI process, the WTRU may use one or more parameters includingparameters that may be related, corresponding, or specific to thetransmission state or CSI process (as described herein) and/or the typeof reported CSI (e.g. whether the CSI feedback may include a combiningindicator, or may be used for a coherent joint transmission ornon-coherent joint transmission). For example, the WTRU may use one ormore of the following example transmission-state-specific (orCSI-case-specific) parameters:

-   -   the assumed PDSCH transmission power from some or each point or        CSI-RS resource (or the assumed ratio of PDSCH EPRE-to-CSI EPRE,        or Pc, for some or each point or non-zero power CSI-RS        resource). For example, for a given non-zero-power CSI-RS        resource, this value may depend on whether the CSI-RS resource        is assumed to correspond to a desired signal or an interfering        signal. For instance, the WTRU may be configured to use a first        value of the ratio of PDSCH EPRE-to-CSI EPRE for CSI processes        or CSI cases in which the CSI-RS resource is assumed to        correspond to a desired signal, and a second value of the ratio        of PDSCH EPRE-to-CSI EPRE for CSI cases in which the CSI-RS        resource is assumed to correspond to an interfering signal. This        may provide a more accurate interference (and CQI) estimation,        perhaps because the pre-coder of an interfering point may not be        designed to maximize the interference power received by the        WTRU, among other reasons. In another example, the WTRU may be        configured to use a first value of the ratio of Pc (PDSCH        EPRE-to-CSI EPRE ratio) for a first CSI process configured with        a non-zero-power CSI-RS and a first interference measurement        resource (CSI-IM). Also, the WTRU may be configured to use a        second value of Pc for a second CSI process configured with the        same non-zero-power CSI-RS and a second interference measurement        resource (CSI-IM). The network may set the Pc values in these        processes such that their difference compensates for any        interference measurement bias stemming from imperfect estimation        of interference for either CSI process;    -   a correction factor to the assumed PDSCH transmission power from        some or each point or CSI process; and/or    -   an offset to the estimated CQI index; or the like.

In one or more embodiments, the use of such transmission-basedparameters (e.g. in combination with a WTRU selection mechanism of thetransmission state or CSI process based on a maximum throughput (or CQI,or rank)) may enable the CSI for respective transmission states or CSIprocesses that may use more resources from the network perspective (orthat may use the reporting of more CSI bits) to be reported if the useof such transmission states or CSI processes may provide a benefit incomparison to less resource-consuming states. In some embodiments, forthe same transmission state or CSI process, different parameters mayalso be applied for different assumed ranks.

For example, the WTRU may be configured to report CSI for up to 2transmission points where the set of transmission states or CSIprocesses that may be reported by the WTRU may include (e.g. using thetransmission points) one or more of the following: a single transmissionfrom the first point (with the second point possibly interfering); asingle transmission from the second point (with the second pointpossibly interfering); joint transmission from both points; and/or thelike.

Embodiments contemplate that the estimated CQI indices for each of thetransmission states or CSI processes may be 8, 6 and 9 respectively in acertain subframe (e.g. in the absence of correction factors), forexample. As such, the WTRU may report CSI for a joint transmission (e.g.which may double the cost of such a transmission from the networkperspective) even though the incremental benefit over a singletransmission may be minimal. In some embodiments, if the method ofapplying correction factors to the assumed PDSCH transmission powerdescribed herein may be used, the WTRU may apply a correction factor of,for example, 0 dB to each single-point transmission states or CSIprocesses and a correction factor of −3 dB to the joint transmissionstate or CSI process. Additionally, such correction factors (e.g. whenapplied) may result in estimated CQI indices of 8, 6, and 6 such thatthe UE may report the CSI corresponding to a single transmission fromthe first point (CQI=8), for example.

Embodiments contemplate that the value(s) of the correction factor thatmay be applied may be defined or provided for some or each certaintransmission states or CSI processes (e.g. 2 dB for a jointtransmission, 0 dB for single-point transmission, 1 dB for single-pointtransmission with muting in other points, or the like). Alternatively,the value(s) of the correction factor may be a function of the number oftransmission points that may not be, or may be assumed to not be,interfering to the WTRU. In one or more embodiments, the value(s) of thecorrection factor may be a function of the number of transmission pointswhich may be assumed to be transmitting to the WTRU, for example.

Embodiments contemplate that the value(s) of the correction factor (orparameters that may be used to derive the correction factors) may alsobe pre-defined. Alternatively, the value(s) of the correction factor (orparameters that may be used to derive the correction factors) may besignaled by the network using higher layer (e.g. RRC) signaling, forexample. Such signaling of the parameters may enable the network toadjust the likelihood of reporting CSI for certain transmission statesor CSI processes based on current conditions such as network load, amongother conditions. For example, if a low system load may be present, theWTRU or WTRUs may report CSI for a joint transmission as there may bespare capacity, perhaps significant spare capacity, in the network. Insuch cases for other considerations, one or more embodiments contemplatethat the correction factor for a joint transmission may be decreased.Alternatively or additionally, one or more embodiments contemplate thatthe correction factor may be increased, perhaps when the system may bemore heavily loaded, among other reasons.

Embodiments contemplate one or more techniques that may be used forproviding the correction factors for each transmission state or CSIprocess. One or more embodiments contemplate that a correction factorfor the assumed ratio (e.g. that may be already signaled) of PDSCH EPREto CSI-RS EPRE may be provided as part of each configured CSI-RSresource (that may be corresponding to a transmission point). Such acorrection factor may be applied for the purpose of estimating CSI for atransmission state or CSI process that may involve a joint transmissionto the WTRU from such a transmission point and at least one additionalpoint, for example. Alternatively, a new value of the assumed ratio ofPDSCH EPRE to CSI-RS EPRE applicable to a joint transmission maydirectly be provided (instead of applying a correction factor to theassumed ratio of PDSCH EPRE to CSI-RS EPRE applicable to a single-pointtransmission). A similar approach may also be used to provide theparameters that may be used for transmission states or CSI processesinvolving a transmission point and muting from at least one othertransmission point, or a transmission state or CSI process involvingmuting from a transmission point.

Alternatively or additionally, embodiments contemplate that a correctionfactor associated with the assumed PDSCH transmission power (e.g. fromeach of the points) may be provided from some allowable transmissionstate or CSI process and/or every allowable transmission state or CSIprocess. For example, instead of explicitly listing each of the possibletransmission states or CSI processes, a correction factor may beprovided as a function of the number of transmission points transmittingto the WTRU and/or the number of transmission points not transmitting toany WTRU (e.g., muting) for any given transmission state or CSI process.In one or more embodiments, a correction factor of 0 dB, 2 dB and 4 dBmay be defined for transmission state(s) or CSI processes involvingtransmission to the WTRU (and/or muting) from, for example, a singletransmission point, two transmission points, and/or three transmissionpoints, etc., respectively. Additional correction factors (e.g. that maybe applied along with the correction factors) for the number of pointstransmitting to the WTRU may be defined for the number of transmissionpoints muting (e.g. not transmitting to a WTRU).

Embodiments contemplate one or more Transmission State or CSI Case orCSI Process configurations for a WTRU. In one or more embodiments, aWTRU may be configured to feedback for several CSI Cases or CSIProcesses. Some or each CSI Case or CSI process may be comprised of adesired signal (e.g., a NZP CSI-RS), an interference resource (e.g., azero-power (ZP) CSI-RS) and possibly other NZP CSI-RS whose receivedpower the WTRU may translate to potential interfering power. The WTRUmay also be configured by one or more higher layers or by DCI to addanother offset to the interference to further refine CQI calculations.In one or more embodiments, the offset may be semi-statically configuredby higher layer signaling. Alternatively or additionally, the offset maybe in a DCI providing a downlink assignment (e.g., a DCI Format1/1A/1B/1C/1D/2/2A/2B/2C). Alternatively or additionally, in one or moreembodiments, the offset may not be explicitly provided to the WTRU.Higher layer signaling, or the downlink assignment may include a flag(with, for example 0 indicating no offset and 1 indicating use of anoffset) instructing the WTRU to use an offset. This offset may becalculated at the WTRU by summing and/or appropriately scaling the RSRPcontributions of points in a CoMP cluster that may not be used for thedesired signal, and/or are not represented in the interferencemeasurement resource and/or are not to be emulated on. In suchconfigurations, the WTRU may be preconfigured with a list of points inits CoMP Resource Management Set which the WTRU may use in thecalculation of the offset, perhaps if the use of such an offset istriggered.

Alternatively or additionally, in some embodiments the WTRU may beconfigured such that some or any points in its CoMP Measurement Set thatmay not be used either for desired signal or for interference emulationmay be considered to be part of the set of points to be used in theoffset. In such scenarios, the WTRU may be provided with a mapping ofpoints in its CoMP Measurement Set and those in the WTRU's CoMP ResourceManagement Set, perhaps in order to determine what RSRP values to use,among other reasons, for example. Alternatively or additionally, higherlayer signaling and/or the appropriate DCI may include a bitmap whichindicates which resources of the CoMP Resource Management Set should beused in the calculation of the offset, for example.

One or more embodiments contemplate that it may be useful for a WTRU toknow whether a NZP CSI-RS in its CoMP Measurement Set represents thesame transmission point as a NZP CSI-RS in its CoMP Resource ManagementSet. Alternatively or additionally, the CoMP Resource Management Set maybe a superset of the CoMP Measurement Set. In such scenarios, the WTRUmay be configured with a CoMP Measurement Set as well as with an extraNZP CSI-RS which may both be combined to create the CoMP ResourceManagement Set. Alternatively or additionally, both sets may beindependently configured, however the NZP CSI-RS used for a transmissionpoint in either set may be the same. In such scenarios, the WTRU mayimplicitly know which NZP CSI-RS in each set are for the sametransmission points. Alternatively or additionally, some or each NZPCSI-RS in the CoMP Resource Management Set may be given an index andthese indices may be indicated to the WTRU when the CoMP ResourceManagement Set is configured, for example. In some embodiments, perhapswhen the network configures the CoMP Measurement Set for the WTRU, itmay provide the NZP CSI-RS configuration as well as an index to identifywhich NZP CSI-RS in the CoMP Resource Management Set may map to the sametransmission point.

Alternatively or additionally, the NZP CSI-RS in the CoMP ResourceManagement Set may be given a predetermined order. In one or moreembodiments, NZP CSI-RS in the CoMP Measurement Set that may also beincluded in the CoMP Measurement Set may be given a flag. In someembodiments, the same ordering of NZP CSI-RS may be used in the CoMPMeasurement Set. For example, the CoMP Resource Management Set may have10 NZP CSI-RS in a pre-determined order. The fourth and seventh NZPCSI-RS may be flagged as being in the CoMP Measurement Set. Given thatthe hierarchy may be kept the same in the CoMP Measurement Set (and insome embodiments perhaps must be kept in the CoMP Measurement Set), thefirst NZP CSI-RS in the CoMP Measurement Set may correspond to thefourth NZP CSI-RS in the CoMP Resource Management Set, and the secondNZP CSI-RS in the CoMP Measurement Set may correspond to the seventh inthe CoMP Resource Management Set. In another example, the ordering maynot be kept in the CoMP Measurement Set, and each NZP CSI-RS configuredin the CoMP Measurement Set may also include a pointer to a NZP CSI-RSin the CoMP Resource Management Set.

Alternatively or additionally, perhaps when the network configures theCoMP Measurement Set, it also may include a combinatorial index r, where

$r = {\sum\limits_{i = 0}^{M - 1}\left\langle \begin{matrix}{N - s_{i}} \\{M - i}\end{matrix} \right\rangle}$

and the set

{s_(i)}_(i = 0)^(M − 1), 1 ≤ s_(i) ≤ N, s_(i) < s_(i + 1)

may contain the M sorted NZP CSI-RS combination indices and

$\left\langle \begin{matrix}x \\y\end{matrix} \right\rangle = \left\{ {\begin{matrix}\begin{pmatrix}x \\y\end{pmatrix} & {x \geq y} \\0 & {x < y}\end{matrix}.} \right.$

Alternatively or additionally, the NZP CSI-RS that may be used in eachset for a transmission point may be different. Embodiments contemplatethat the configurations may lead to an overlap of same time/frequencyREs used in the same subframes. In such scenarios, the WTRU may assume,perhaps implicitly, that any two NZP CSI-RS that may share any RE arefrom the same transmission point.

Embodiments contemplate Primary Transmission State or CSI Case or CSIProcess configurations. For CSI reporting, among other reasons, one ormore embodiments contemplate that a WTRU may be configured with aprimary Transmission State (or CSI Case or CSI Process). The primary CSIProcess may be used for fallback operation (e.g., in the case where theWTRU cannot achieve CoMP operation), default operation (e.g., in thecase where a WTRU is not dynamically or semi-statically configured witha CSI Process) or for priority operation (e.g., in the case where a WTRUcannot accomplish the appropriate feedback for multiple CSI Process, itmay choose to feedback for the first priority CSI Process). Embodimentscontemplate that a WTRU may have a different CSI Process for each offallback, default and priority operation. When configuring a WTRU with aCSI Process, the network may also indicate (e.g., by use of a bitflag)whether the process may be used for any of fallback, default and/orpriority. Alternatively or additionally, the WTRU may be configured witha single CSI Process based on CRS, and it may thus assume this to be thefallback, default and/or high priority CSI Process. Alternatively oradditionally, the WTRU may be configured with a single CSI Process thathas the NZP CSI-RS of its serving cell as the desired signal. In suchscenarios, the WTRU may assume that such a CSI Process is the fallback,default and/or high priority CSI Process, for example.

Alternatively or additionally, the WTRU may be configured such that theCSI Process to use as the fallback, default and/or high priority may bethe one whose transmission point was used in the most recenttransmission. Alternatively or additionally, there may be a flag in theDCI used for downlink assignment indicating that the transmission pointused for the scheduled assignment may, at least until further notice,indicate or imply that the CSI Process using such a transmission pointas its desired signal, be configured as the fallback, default and/orhigh priority.

Embodiments contemplate that a WTRU that may be configured to report CSIfor one or a plurality of transmission points (or CSI-RS-resources) mayhave to report CSI for a subset of these transmission points in aparticular subframe, and in some embodiments perhaps only a subset ofthese transmission points in a particular subframe. In addition, a WTRUthat may be configured to report CSI for a plurality of CSI cases(transmission states or CSI processes) may report CSI for a subset ofCSI cases in a particular subframe (and in some embodiments perhaps onlysuch a subset). This may be because of the following reasons:

-   -   The transmission state or CSI process recommended by the WTRU,        or requested by the network, involves a transmission from a        subset of transmission points, and in some embodiments perhaps        only involves a transmission from a subset of transmission        points;    -   Due to payload constraints, for instance in case of periodic        reporting, the WTRU may be capable of reporting a feedback        component for a subset of transmission points or        CSI-RS-resources or CSI cases, and in some embodiments may be        capable of such reporting only in a particular subframe.        Embodiments contemplate one or more methods described herein of        indicating to which subset or subsets of transmission points a        report containing CSI feedback components may apply.

Embodiments contemplate that when the WTRU may report feedback formultiple cells, a point indicator (PI) and/or CSI-RS-resource indicatorand/or CSI case or CSI process indicator may indicate, and perhapsexplicitly indicate, the transmission point or set of transmissionpoints or CSI case or CSI processes that the feedback report is for. Theindicator may include the PCI of the transmission point. The indicatormay include an index associated to the CSI case. For instance the indexcould correspond to the order of the CSI case or CSI process in the CSIconfiguration (plus possibly an offset). The indicator may include arealization of a bitmap provided by the network, where a 1 in a specificbit location may represent a specific transmission point orCSI-RS-resource configured by higher layers. The bitmap may be signaledto the WTRU by higher layer RRC signaling or may be provided in anuplink DCI (triggering aperiodic feedback on PUSCH) or a Random AccessResponse Grant, for example. The bitmap may be based on the CoMPmeasurement set and may be static, semi-static, or dynamic. Theindicator may include n-bit stream, where possible n-tuple may representone of the 2^(n) transmission points. The indicator may include anordered list of indices, wherein some indices or each index of the list,possibly in binary format, may indicate a specific transmission point orconfigured CSI-RS-resource. This type of point indicator may be usefulto provide ranking information between points. In one or moreembodiments, the indicator may indicate a set of size M (out of Npossible transmission points), for instance, for the purpose ofselecting M recommended points, for example. The indicator may includean indicator that may relate to a specific point in a TSV. The indicatormay include a combinatorial index r, where

$r = {\sum\limits_{i = 0}^{M - 1}\left\langle \begin{matrix}{N - s_{i}} \\{M - i}\end{matrix} \right\rangle}$

and the set

{s_(i)}_(i = 0)^(M − 1), 1 ≤ s_(i) ≤ N, s_(i) < s_(i + 1)

may include the M sorted transmission point indices and

$\left\langle \begin{matrix}x \\y\end{matrix} \right\rangle = \left\{ {\begin{matrix}\begin{pmatrix}x \\y\end{pmatrix} & {x \geq y} \\0 & {x < y}\end{matrix}.} \right.$

For some or each specific feedback, which transmission point that afeedback report may be for may be determined based on an indicator.

Alternatively or additionally, embodiments contemplate that a subset oftransmission points and/or a CSI case or CSI process may be jointlyindicated with a subset of selected subbands into apoint-subband-indicator (PSI). The PSI may include one or more of thefollowing:

-   -   A bitmap where a 1 in a specific bit location may represent a        specific combination of transmission point and subband, or of a        CSI case or CSI process and subband; and/or    -   For the case where the WTRU may indicate a set of size M (out of        N possible combinations of transmission point and subband), for        instance, for the purpose of selecting M recommended        combinations of points and subbands (or of CSI case or CSI        process and subband), a combinatorial index r may be used, where

$r = {\sum\limits_{i = 0}^{M - 1}\left\langle \begin{matrix}{N - s_{i}} \\{M - i}\end{matrix} \right\rangle}$

and the set

{s_(i)}_(i = 0)^(M − 1), 1 ≤ s_(i) ≤ N, s_(i) < s_(i + 1)

contains the M sorted point-subband combination indices and

$\left\langle \begin{matrix}x \\y\end{matrix} \right\rangle = \left\{ {\begin{matrix}\begin{pmatrix}x \\y\end{pmatrix} & {x \geq y} \\0 & {x < y}\end{matrix}.} \right.$

Embodiments contemplate that the PI or PSI may be transmitted in one ormore of:

-   -   The same subframe as the feedback component it may apply to. In        case multiple PI's or PSI's are transmitted in a same subframe,        the association between a PI (or PSI) and the feedback        information may be pre-determined by the bit order; and/or    -   A subframe occurring before the subframe in which the feedback        information is transmitted, and in some embodiments according to        a pre-determined rule. In other words, the subset of        transmission points may correspond to the most recently        transmitted PI or PSI. For instance, the WTRU may transmit PI or        PSI in a first set of pre-determined subframes (e.g.        periodically) and the related feedback in a second set of        pre-determined subframes. The PI or PSI applicable to the        feedback transmitted in a given subframe of the second set may        be the most recently transmitted PI or PSI within the first set,        for example.        Embodiments contemplate that at least one of the PI or PSI may        allow saving on feedback overhead, as the WTRU may feedback        reports for the strongest n points or CSI cases (and in some        embodiments only for the strongest n points or CSI cases) and        may drop the feedback reports for any other point or CSI case.        The feedback reports may include PI to indicate to the network        for which transmission point a feedback is for.

The indication of which transmission point the feedback may be for—mayor may not be explicit. For example, the transmission point may beimplicitly determined based on a transmission point specific scramblingor of a CSI case-specific scrambling. In one or more embodiments, thesubset of transmission points or CSI case or CSI process may beimplicitly and/or uniquely determined from the timing of the subframe(frame and subframe number) where the feedback is transmitted. The WTRUmay transmit a feedback component for a subset of transmission points(or CSI cases) in a first subframe under the condition that the WTRUtransmitted an indication that feedback would be provided for thissubset of transmission points (or CSI cases) in a second previoussubframe. In some embodiments, the WTRU may transmit a feedbackcomponent for a subset of transmission points (or CSI cases) in a firstsubframe only under the condition that the WTRU transmitted anindication that feedback would be provided for this subset oftransmission points (or CSI cases) in a second previous subframe. Thesecond subframe may be the most recent subframe in a set ofpre-determined subframes, for example. The indication may include asingle bit, a PI or PSI, and/or it may be encoded as a specificcodepoint of a heretofore undefined report type or a modified reporttype.

In one or more embodiments, the subset of transmission points may beimplicitly determined from the most recently transmitted transmissionstate indicator (TSI), CSI case or CSI process indicator, PI or PSI aswell as the subframe timing according to a pre-configured set of rules,for instance according to a specific mode of periodic reporting. By wayof example, within a set of subframes occurring periodically, thetransmission point or CSI case or CSI process for which feedback isprovided may be cycled among the transmission points or CSI casesindicated in the most recently transmitted PI. In another example, thetransmission point or CSI case or CSI process may correspond to thefirst indicated transmission point or CSI case or CSI process in themost recently transmitted PI in a first set of subframes, and to thesecond indicated transmission point or CSI case or CSI process in themost recently transmitted PI in a second set of subframes. This may beuseful for a number of reasons, such as for example if it is desired totransmit more frequently the feedback for the first transmission pointor CSI case or CSI process than for the second transmission point or CSIcase.

Embodiments contemplate that, in one or more of the aforementionedtechniques, it is also possible that the subset of transmission pointsto which a certain feedback component applies may be additionallydependent on the type of feedback (CQI, PMI or RI). For instance, theWTRU may report in a given subframe an aggregated CQI for a transmissionfrom two points along with a per-point PMI for one of the two points.This may be useful for a number of reasons, such as for example in caseper-point PMI for the other point has already been provided in aprevious subframe.

One or more embodiments contemplate the selection of PUCCH Format 3resources. In some embodiments, perhaps when a WTRU may be configured toreport for multiple CSIs and potentially for multiple A/N in the samesubframe, the WTRU may use PUCCH Format 3. In order to determine theresources to be used for PUCCH Format 3, among other reasons, the WTRUmay be semi-statically configured by higher layers with appropriateresources. Alternatively or additionally, the WTRU may be configuredwith multiple Virtual Cell IDs (VCID) for PUCCH. In some embodiments,the WTRU may be configured with a set of resources that may be tied tosome VCID or to every VCID. In some embodiments, perhaps when thenetwork dynamically configures the WTRU to a specific VCID for PUCCH, itmay be either explicitly or implicitly also configuring the requiredresources. Alternatively or additionally, a WTRU may be configured withan ARI mapping by higher layers. In one or more embodiments, this ARImay be valid even when there is no Scell configured. Embodimentscontemplate that an Ack/Nack resource indicator (ARI) may be a field inthe DCI which may be used to indicate a PUCCH resource index.Embodiments contemplate that the field may be an existing field such asfor example a TPC field (e.g., perhaps when received from a DCIindicating an Scell assignment). Embodiments contemplate that ARImapping may include a table that links some values or each value of theARI to a PUCCH resource index (e.g., configured in RRC). In one or moreembodiments, the ARI may be coupled with the TPC Command in DCI Formatof the corresponding PDCCH. Alternatively or additionally, a new orfresh ARI may be included in the DCI Format of the corresponding PDCCH.Stated somewhat differently, embodiments contemplate a new (e.g.,heretofore unused) standalone ARI field and/or the use of the TPC fieldas an ARI field, for example. Alternatively or additionally, the WTRUmay be configured to track multiple TPC commands for different receptionpoints. In such scenarios, there may be an identifier tied to the TPCcontrol. This identifier can be used by the WTRUI to also determinewhich PUCCH Format 3 resources to use. Alternatively or additionally,for some or each Transmission state or CSI Case or CSI Process, a WTRUmay have a set of PUCCH Format 3 resources configured, for example.

Alternatively or additionally, embodiments contemplate that, perhaps incase of collision(s) between the transmission of a periodic report onPUCCH and of HARQ A/N in a given subframe, among other reasons, the WTRUmay multiplex CSI information with HARQ A/N information on the PUCCHformat 3 resources that may be configured for periodic CSI reporting. Insome embodiments, the periodic CSI information may be compressed, forinstance by reducing the granularity of the PMI information. Also, insome embodiments, the HARQ A/N information may also be compressed bybundling (e.g., AND operation over HARQ A/N bits). Alternatively oradditionally, where the WTRU may be configured to use PUCCH format 3 forHARQ A/N transmission in the subframe where the collision(s) may occur(for instance, in case carrier aggregation is configured and anassignment from a secondary cell exists), the transmission ofmultiplexed periodic CSI and HARQ A/N information may take place overthe PUCCH resource indicated by the A/N resource indicator of thesecondary cell assignment (e.g., the TPC bits in the DCI containing theassignment).

Embodiments contemplate techniques for determining which of theabove-described CSI feedback components and types may be reported to thenetwork and/or in which sub-frame(s). Also, embodiments contemplate oneor more techniques for selecting contents of one or more aperiodic CSIreports. In an example, a WTRU may report at least one CSI feedbackcomponent of at least (if applicable) one type or sub-type in a givensubframe (n) if it received an aperiodic CSI request in a previoussubframe (n-k) where k may be pre-defined or signaled, for example. Inan embodiment, an aperiodic CSI request in subframe (n) may trigger aWTRU to report at least one CSI feedback component of at least (ifapplicable) one type or sub-type, in different subframes for differenttransmission points or CSI cases. For example, feedback for transmissionpoint 1 may be transmitted in subframe n+k₁, and feedback fortransmission point 2 may be transmitted in subframe n+k₂, and so on. Theset of {k₁, k₂, . . . } may be pre-defined or signaled, for example.

Embodiments contemplate that, for a given set of transmission points orCSI cases, the set of CSI components, types and sub-types that arereported, as well as associated conditions (described herein), may bedetermined according to at least one of:

-   -   A characteristic of the downlink transmission containing the        aperiodic CSI request, such as: an indication from the downlink        control signaling (such as PDCCH) containing the aperiodic CSI        request for the WTRU. For example, the indication may be        provided by specific codepoint(s) of an existing field, such as        the CSI request field, or the carrier indication filed, or        possibly of a field in a contemplated but heretofore not defined        DCI format; the set of antenna ports or reference signals used        for the transmission of the downlink control signaling (CRS or        DM-RS in case of E-PDCCH for example); whether the downlink        control signaling is received from PDCCH or E-PDCCH; the search        space (e.g. common search space or WTRU-specific search space)        in which the downlink control signaling may be decoded; the PRB,        E-REG, or E-CCE in which the downlink control signaling may be        decoded in case of E-PDCCH; another field of the DCI that may be        reused or reinterpreted, such as the IMCS, the cyclic shift        field, the frequency allocation field, the frequency hopping        field or the aperiodic SRS field. For instance, the aperiodic        SRS field may be reinterpreted as an extension to the CSI        request field in case the CSI request field may be set to one of        a subset of values (e.g. different than 0). In this case,        functionality associated to the reinterpreted field may be        modified. For instance, the WTRU may not trigger an aperiodic        SRS transmission regardless of the value of this field; the RNTI        used for successfully decoding the downlink control signaling;        and/or the serving cell or CSI-RS resource corresponding to the        point from which the downlink control signaling containing the        aperiodic CSI request is transmitted. For instance, the        transmission states or CSI case(s) or CSI processes that are        reported may correspond to one or more CSI case or CSI process        in which it may be assumed that this CSI-RS resource transmits a        desired signal;    -   The timing of the subframe where the request may be received        (n-k) or of the subframe where the CSI is to be reported (n),        which may be expressed in terms of a system frame number and/or        subframe number. For instance, in the case of N CSI cases, the        set of subframes for the jth CSI case or CSI process may be        defined as subframes satisfying (10 Nf+Ns+offset) modulo N=j,        where Nf may be the system frame number, Ns may be the subframe        number and offset may be a parameter configured by higher        layers;    -   A characteristic of the uplink transmission indicated by the        downlink control signaling that contained the aperiodic CSI        request. For instance, perhaps depending on the size of the        resource block allocation (grant), the WTRI may report CSI for a        single CSI case or CSI process (if the size is below a        threshold, for example) or for more than one CSI case or CSI        process (if the size is above a threshold, for example);    -   Higher layer signaling (e.g. RRC configuration);    -   The (PUSCH) CSI reporting mode;    -   Whether some or all transmission points are transmitting same        (dependent) or different (independent) data; and/or    -   A combination of the above, such as reserving a codepoint of the        aperiodic CSI request field to indicate that the set of CSI        components or types/sub-types to be reported corresponds to the        timing of the subframe where the request is received.

Embodiments contemplate one or more examples of associated conditionsthat may be indicated (such as but not limited to):

-   -   Whether a reported per-point CQI_(k) is unconditioned or        conditioned, and possibly, in the latter case, whether the        condition is for minimum interference (such as “no transmission”        or “zero precoder”) or maximum interference;    -   Whether a coherent or non-coherent aggregated CQI (or joint CQI)        should be reported;    -   Whether a combining indicator i_(comb) or a combining matrix        W_(comb) should be reported;    -   Whether the reports are wideband or for specific sub-bands;    -   Whether long-term (first) precoding matrix indication is        reported or short-term (second) precoding matrix indication is        reported;    -   Whether the interference precoding matrix corresponds to maximum        or minimum interference;    -   Whether the set of precoding matrices W_(k)′ corresponds to a        set from which the transmission point should or should not        select a precoding matrix; and/or    -   An indication of the Transmission State Vector (or a        transmission state indicator, TSI) or CSI case or CSI process.

Embodiments contemplate one or more techniques for the selection of thesubset of transmission states, CSI processes, or CSI cases for whichaperiodic feedback may be provided. In one or more embodiments, thesubset of CSI cases may be selected according to the outcome of at leastone of the previously described selection methods. The outcome of aselection method may correspond for instance to the value of a CSIrequest field or another field, or to a function of the subframe timing,or to whether the control signaling is decoded in a common search spaceor a UE-specific search space, or any function or combination thereof.For example, an outcome may be defined by the combination of a certainvalue of a CSI request field and/or of a certain value of a carrierindication field. In another example, an outcome may be defined by thecombination of a certain value of a CSI request field and/or of acertain value of the subframe number modulo 2.

Embodiments contemplate that a subset of CSI cases or CSI processescorresponding to a specific outcome may be defined using at least one ofa number of contemplated techniques. In one or more embodiments, thesubset of CSI cases may be predetermined for at least one possibleoutcome of the selection method. For instance, for a selection based onthe value of a CSI request field, a first codepoint may correspond tosome or all CSI cases (and in some embodiments may always socorrespond), a second codepoint may correspond to the nth configured CSIcase or CSI process (and in some embodiments may always so correspond),etc.

In one or more embodiments, the subset of CSI cases may be provided,perhaps explicitly, by higher layers for at least one possible outcomeof the selection method. For instance, for a selection based on thevalue of a CSI request field, a codepoint may correspond to a subset ofconfigured CSI cases indicated by higher layers.

In one or more embodiments, the subset of CSI cases for at least onepossible outcome of the selection technique may be the subset of CSIcases for which a specific CSI-RS resource may be assumed to be adesired signal. The specific CSI-RS resource may be indicated by higherlayers, or may be based on its order in the configuration ofnon-zero-power CSI-RS resources. Such embodiments may, among otherthings, allow the network to obtain the CSI information for some or allCSI cases corresponding a transmission of a desired signal from aspecific point in a single subframe.

In one or more embodiments, the subset of CSI cases for at least onepossible outcome of the selection technique may be the subset of CSIcases for which a specific CSI-RS resource may be assumed to beinterfering (or not interfering), or for which at least one CSI-RSresource may be assumed to be interfering (or not interfering), or forwhich no CSI-RS resource may be assumed to be interfering. The specificCSI-RS resource may be indicated by higher layers, or may be based onits order in the configuration of non-zero-power CSI-RS resources. Suchembodiments may, among other things, allow the network to obtain therelevant CSI information (and in some embodiments perhaps only therelevant CSI information) when it may be already known that a certainpoint would be interfering (or not interfering). The set of possibleoutcomes to which this subset of CSI cases corresponds may possibly bedefined by a new field or by a new bit(s) of an extended CSI requestfield.

In one or more embodiments, the subset of CSI cases for at least onepossible outcome of the selection technique may be CSI cases selected bythe WTRU according to a TSI (or CSI case) selection method describedherein. For instance, a codepoint of a CSI request field may correspondto reporting CSI for the CSI case or CSI process for which CQI may bethe highest. In such embodiments, the WTRU may report an indication ofthe selected CSI case or CSI process (such as a TSI or a PI) for some oreach reported CSI case or CSI process.

In one or more embodiments, the subset of CSI cases for at least onepossible outcome of the selection technique may be determined by cyclingthrough multiple subsets of CSI cases. For instance, two subsets of CSIcases may be defined. At some times, or perhaps every time, the value ofthe CSI request field may be a certain codepoint, the WTRU may switchthe subset of CSI cases for which it is providing the report. In suchembodiments, the WTRU may report an indication of the selected CSI cases(or one or more subsets thereof) to prevent ambiguity, among otherreasons.

In one or more embodiments, the subset of CSI cases for at least onepossible outcome of the selection technique (and in some embodiments,possibly all outcomes) may be restricted to the subset of CSI cases forwhich the corresponding serving cell may be the serving cell of the ULtransmission in which the CSI is reported, possibly as indicated by acarrier indicator field. In such embodiments, the WTRU may be configuredwith more than one cell (carrier aggregation), possibly in combinationwith one of the above techniques described herein. In some embodiments,a first codepoint of the CSI request field may be associated to a firstsubset of configured CSI processes that may be indicated by one or morehigher layers for this codepoint. The subset of CSI processes that maybe reported when a CSI request is received with this value of thecodepoint may be the subset of CSI processes, within the subset ofconfigured CSI processes indicated by one or more higher layers, forwhich the corresponding serving cell is the serving cell of the ULtransmission in which the CSI is reported. A second codepoint of the CSIrequest field may be associated to a second subset of configured CSIprocesses that may be indicated by one or more higher layers for thiscodepoint. The subset of CSI processes that may be reported when a CSIrequest is received with this value of the codepoint may be the subsetof configured CSI processes indicated by one or more higher layers,perhaps irrespective of the serving cell of the UL transmission in whichthe CSI may be reported, for example.

In one or more embodiments, the subset of CSI cases for at least onepossible outcome of the selection technique may be the subset of CSIcases that are identified, for some or each serving cell, as the primaryCSI case or CSI process among the CSI cases configured for this servingcell. For instance, for one codepoint of the CSI request the subset ofCSI cases that are reported may be the subset of primary CSI cases forsome or all serving cells.

Embodiments contemplate one or more examples of sets of CSI components,types and sub-types that may be reported following an aperiodic request,perhaps in an aperiodic feedback report. Aggregated CSI or Joint CSI mayinclude one or more of Common (or joint) rank indication (RI_(joint)),per-point rank indication (RI_(k)) for specific transmission point k,such as a transmission point identified as a “serving transmissionpoint”, aggregated CQI (or joint CQI) (CQI_(joint)) for at least onecodeword, and/or Global precoding matrix indicator(s), and the like.Aggregated CSI (or Joint CSI) may include one or more of an indicator ofthe transmission state or CSI process, or transmission state indicator(TSI) or CSI process indicator. Aggregated CSI (or Joint CSI) mayinclude a primary per-point CQI and at least one delta per-point CQI(e.g., for secondary transmission points). Aggregated CSI (or Joint CSI)may include a muting pattern indicative of which points the WTRU mayassume are blanked for the feedback reported. Aggregated CSI (or JointCSI) may include a vector of point indicator (PI). One or moreembodiments contemplate that the PI may map to the points in the CSIprocess or transmission state vector (indicated by TSI). Aggregated CSI(or Joint CSI) may include one or more associated conditions. Per-pointCSI for a subset of transmission points may include a per-point rankindication (RI_(k)), a per-point CQI (CQI_(k)) for at least onecodeword, a per-point (or local) precoding matrix indicator(s), a set ofprecoding matrix indicator(s) W_(k)′, a PI, the corresponding element ofthe CSI process or transmission state vector, a primary CQI or a deltaCQI (associated to a primary CQI), and/or at least one associatedcondition for each transmission point.

Embodiments contemplate that, for reporting modes where the feedbacktype may be on WTRU selected sub-bands, the WTRU may also indicatewhether some transmission points, or perhaps each transmission point,may have the same subset of sub-bands, and/or if they are orthogonal toeach other, and/or if they overlap, for example. In one or moreembodiments, this may be realized by transmitting a point-subbandindicator (PSI) as described herein. For a number of reasons, such asfor example when there may be at least a partial overlap of subsets, theWTRU may provide a combination of Aggregated CSI (or Joint) CSI and, insome embodiments, as well as per-point CSI. Embodiments contemplate thata bitmap may be used to indicate to the transmission points which typeof CSI may be applicable to which sub-bands.

Embodiments contemplate that, whether the WTRU selects a common set ofsubbands for all points, or a separate set of subbands for each point,may be configured by higher layers. One or more such configurations maybe provided by the network, perhaps in some embodiments according to theintended type of coordinated transmission. For instance, the WTRU may beconfigured to select a common set of subbands for some or all points,for example in case the network intends to use joint transmission.Alternatively or additionally, the WTRU may be configured to select aseparate set of subbands for some points or for each point, for examplein case the network intends to use dynamic point selection.

Embodiments contemplate that the report types can be fed back usingpre-existing modes where different CSI reports may be mapped to existingfields. For example, aperiodic PUSCH feedback mode 1-2 may be reusedwhere—perhaps instead of feeding back multiple PMI representing one persub-band—the WTRU may feedback multiple PMIs representing one pertransmission point or per CSI case.

In one or more embodiments, the WTRU may be triggered by the networkwith aperiodic feedback such that the WTRU may provide the new rankingof transmission points to modify the periodicity/offsets of some or eachpoint. The WTRU may use such parameters in periodic feedbacks until anew (or fresh) aperiodic feedback is triggered. Embodiments contemplatethat the aperiodic CSI reporting for CoMP may contain any combination ofat least one of the following:

-   -   The Transmission State Indicator (TSI), or CSI process        indicator, or CSI case indicator;    -   The Point Indicator (PI);    -   The combinatorial index indicating the UE selected M subbands;    -   The combinatorial index indicating the UE selected N points;    -   The combinatorial index indicating the UE selected point-subband        combinations (PSI);    -   The aggregated or per point RI (RIa or RIp);    -   The aggregated or per-point wideband CQI (W-CQIa or W-CQIp);    -   The aggregated or per-point subband CQI (S-CQIa or S-CQIp);    -   The aggregated or per-point M-band CQI (M-CQIa or M-CQIp);    -   The aggregated or per-point wideband PMI (W-PMIa or W-PMIp);    -   The aggregated or per-point wideband first PMI (W-PMI1a or        W-PMI1p). Where PMI1 corresponds to the first precoding matrix        in the two-PMI method introduced in Rel-10;    -   The aggregated or per-point wideband second PMI (W-PMI2a or        W-PMI2p). Where the PMI2 corresponds to the second precoding        matrix in the two-PMI method introduced in Rel-10;    -   The aggregated or per-point subband PMI (S-PMIa or S-PMIp);    -   The aggregated or per-point subband first PMI (S-PMI1a or        S-PMI1p);    -   The aggregated or per-point subband second PMI (S-PMI2a or        S-PMI2p);    -   The aggregated or per-point M-band PMI (M-PMIa or M-PMIp);    -   The aggregated or per-point M-band first PMI (M-PMI1a or        M-PMI1p);    -   The aggregated or per-point M-band second PMI (M-PMI2a or        M-PMI2p);    -   The wideband inter-point phase indicator;    -   The subband inter-point phase indicator;    -   The M-band inter-point phase indicator;        Embodiments contemplate that inter-point phase indicators        (wideband, subband and/or M-band, for example) may be linked to        multiple phase values in various situations such as for example        a case where there are more than 2 cooperating points.

Embodiments contemplate that the Rel-10 aperiodic reporting modes can bemodified and/or augmented to accommodate efficient CoMP feedbackreporting. Modes may be defined as Mode x-y, where x may indicatewhether the CQI feedback is for wideband, network configured subbands,or WTRU-selected subbands. Also, y may indicate whether there is no PMIfeedback, single PMI feedback, or multiple PMI feedback. In one or moreembodiments, one or more heretofore undefined dimensions can be added tosome or all of the modes to indicate an assumption on the selection ofTSV such as whether the feedback is for a) some or all points in theCoMP measurement set, b) network selected TSV or c) WTRU selected TSV.As an example, the contemplated mode could take the form of Mode x-y-z,where z may represent the assumption on the selection of TSV. In eithersome or in all three of the point selection assumptions, the WTRU may beinstructed to provide aggregated or per-point feedback for eachindividual report type. The aperiodic CQI reporting mode may beconfigured by higher-layer signaling (for example in the parametercqi-ReportModeAperiodic).

In one or more embodiments, the existing aperiodic CSI reporting modescan be reused and may be applicable to any of the three assumptionspertaining to TSV. In such a case, either the uplink DCI or RandomAccess Response Grant (that may be used to trigger aperiodic feedback)can be used to instruct the WTRU of the assumption on the selection ofTSV (some or all points, network-selected TSV, and/or UE-selected TSV).In the case of network-selected TSV, the aperiodic feedback trigger mayalso include the network-selected TSI. The TSI may be included as anextension to the CSI request field, for example. The aperiodic feedbacktrigger (e.g., the uplink DCI or the Random Access Response Grant) canalso indicate whether aggregated or per-point feedback may be requiredfor some or each individual report type.

In embodiments in which the WTRU may select the TSV (or CSI case), theaperiodic feedback report may include the TSI as well as the PI and/orPSI. Embodiments contemplate that the PI in such situations may be forscenarios where the WTRU may have many points selected as transmittingin the TSV and may use a specific aperiodic feedback for a subset of thetransmitting points. In such a case, even though one aperiodic feedbackmay not include feedback for some or all points in the TSV, theaggregated CQI may be conditioned on the overall TSV or on just thepoints indicated by the PI(s).

Embodiments contemplate that a hierarchy of points may be providedeither by the WTRU or by the network (based on for example rankingper-point CQI, for example). This hierarchy may be used such that someor all feedback reports for points other than the highest ranked pointmay be differential to the feedback report of the highest ranked point,for example.

Embodiments contemplate one or more techniques for overhead reduction(aperiodic and periodic CSI reporting). Embodiments contemplate that itmay be possible to reduce overhead of CSI reporting by taking advantageof the expected correlation between certain components of CSI feedbackbetween different cases. One or more embodiments described herein may beapplied to at least one or the following cases:

-   -   In case CSI for more than one CSI case or CSI process are        reported in the same aperiodic report;    -   In case CSI for more than one CSI case or CSI process are        reported in the same periodic report instance (subframe); and/or    -   In case periodic CSI instance are configured for more than one        CSI cases or CSI processes.

In one or more embodiments, the WTRU may report once certain feedbackcomponents which may be correlated or assumed identical between thereported CSI cases (and in some embodiments perhaps only once certainfeedback components which may be correlated or assumed identical betweenthe reported CSI cases). For example, the per-point PMI corresponding toa certain CSI-RS resource may be reported if the CSI cases have thissame CSI-RS resource assumed as desired signal, or if it is indicated byhigher layers that a common PMI is used for the reported CSI cases (andperhaps in some embodiments reported only once if so). In case theoptimal per-point PMI may not be the same for two CSI cases that areconfigured to report the same PMI, the reported PMI may be the one thatresults in a maximum CQI for any of the CSI cases. Alternatively oradditionally, the reported PMI may be the one corresponding to a CSIcase or CSI process according to a priority rule, possibly determined byhigher layers, for example.

Similarly, one or more embodiments contemplate that the RI may bereported, in some embodiments perhaps once, if the CSI processes mayhave the same CSI-RS resource assumed as interfering signal, and/or ifit is indicated by higher layers that a common RI may be used for thereported CSI processes (and in some embodiments perhaps reported onlyonce if so). In case the optimal RI may not be the same for two CSIcases that are configured to report the same RI, the reported RI may bea maximum (or the minimum) between the values. Alternatively oradditionally, the reported RI may be the one corresponding to a CSIprocess perhaps according to a priority rule, possibly determined byhigher layers, for example. For instance, the WTRU may be configuredsuch that the reported RI for a first CSI process may be constrained tobe the same as the reported RI for a second CSI process, wherein thesecond CSI process may be referred to as a “RI-reference process” of thefirst CSI process. In such scenarios, the RI may be reported, perhapsonce, if the configured reporting instances for the rank indication maybe the same for both processes, among other reasons. In someembodiments, this may be realized, for instance, if the configuredreporting instances for the rank indication may be the same for bothprocesses. In such scenarios, the RI report of the first CSI process maybe dropped according to a priority rule, such that the RI applicable toboth processes may be reported in a single set of reporting instances.

Alternatively or additionally, embodiments contemplate that the WTRU mayreport a difference between the feedback component (e.g. CQI) of a firstCSI case or CSI process and of a second CSI or CSI process case in placeof reporting the absolute value of the feedback component of the secondCSI case or CSI process. Such embodiments may be useful if, among otherreasons, the difference between values may be expected to be smallerthan one of the absolute values. One or more such embodiments may beapplied perhaps if certain conditions may be met, such as at least oneof:

-   -   both CSI cases use the same CSI-RS resource(s) assumed as        interfering signal;    -   both CSI cases use the same CSI-RS resource(s) assumed as        desired signal; and/or    -   it is indicated from higher layers that the second CSI case or        CSI process may report a differential feedback component from        the first CSI case or CSI process, or the like.

Embodiments contemplate one or more techniques that may be used in thereporting of periodic CSI of a WTRU that may be configured with multipletransmission points or CSI-RS-resources.

In one or more embodiments, a WTRU may report CSI periodically accordingto a configured (PUCCH) CSI reporting mode and/or sub-mode, for example.The reporting mode and/or sub-mode may define which pre-determinedreport types may be transmitted in which reporting instances.

Embodiments contemplate that a WTRU may report at least one CSIcomponent of at least (if applicable) one type or sub-type, possibly incombination with at least one associated condition, and/or additionaltype indication(s) as described herein, in an existing report type or ina previously undefined report type which may be transmitted as part of amodified or in a previously undefined reporting mode. For example, thefollowing report types may be defined as:

-   -   Combining indicator i_(comb);    -   Common (or Joint) rank indication RI_(joint) with existing        precoding type indication (PTI) or presently defined type        indication (see below);    -   First (long-term) per-point combining indicator i_(1kcomb)        combined with first (long-term) per-point precoding indicator        i_(1k);    -   First (long-term) per-point combining indicator i_(1kcomb)        combined with common (or joint) rank indication RI_(joint);    -   First (long-term) per-point combining indicator i_(1kcomb)        combined with first (long-term) per-point precoding indicator        i_(1k) and common (or joint) rank indication RI_(joint);    -   Second (short-term) per-point combining indicator i_(2kcomb)        combined with second (short-term) per-point local precoding        indicator i_(2k);    -   Global (or aggregated) precoding matrix indicator, including        per-point indicators i_(1k), i_(2k) for each transmission point        and combining indicator i_(comb); and/or    -   An indicator of whether CSI feedback for a given transmission        point or CSI-RS-resource (or set thereof) may be subsequently be        reported.

The WTRU may report at least one transmission state indicator (TSI) orCSI process indicator. The WTRU may send different reports to reportfeedback for different TSI(s). The WTRU may send different reports toreport feedback for different sets of TSI(s). In one or moreembodiments, the sets of TSIs may overlap. The reports may be sent withtheir own periodicity and subframe offset(s), for example.

In one or more embodiments, the indication of which point a feedbackreport may be for may be jointly transmitted with another report. As anexample, the rank and point indicator may be jointly transmitted in apreviously undefined report type. The single value may correspond to,Rank 1, using point #1 (and in some embodiments perhaps only point #1);Rank 2, using point #1 (and in some embodiments perhaps only point #1);Rank 1, using point #2 (and in some embodiments perhaps only point #2);and/or Rank 2, using point #2 (and in some embodiments perhaps onlypoint #2), and/or the like.

The joint report may include a phase correction value that may providefeedback information for JT CoMP. For example, the joint report mayinclude Rank 1, using point #1/#2 with phase correction θ₁; Rank 1,using point #1/#2 with phase correction θ₂, and the like. The jointreport may include Rank 1, using point #1/#2 with phase correctionθ_(n); Rank 2, using point #1/#2 with phase correction θ₁; Rank 2, usingpoint #1/#2 with phase correction θ₂, and the like. The joint report mayinclude Rank 2, using point #1/#2 with phase correction θ_(n); Rank 2,using point #1/#2 with each point sending independent data, and thelike.

One or more combinations of the above two sets of values may also beused for a system that supports any combination of JT and DPS.Furthermore, for a non-coherent system, the phase correction may beremoved from the joint report. The identification of point #1 and point#2 may be previously fed back in another report type (such as the PI,for example).

The PI may be transmitted jointly with reports for that cell. In one ormore embodiments, the PI may be transmitted once. The eNB may assumethat until a further PI is transmitted, feedback reports may be for thattransmission point. In one or more embodiments, the WTRU may feedbackthe PI at regular intervals, for example, using a specificperiod/subframe offset. The WTRU may feedback the PI even if the PI hasnot changed. This may reduce the effect of error propagation (e.g. whenan incorrect PI is decoded at the eNB).

In one or more embodiments, the PI may be transmitted in the place ofthe RI. For example, the PI/RI report may include a flag to indicatewhether the PI/RI report type may be for PI or RI. For example, theremay be a pre-configured pattern determining whether the report is for RIor PI. The pre-configured pattern may indicate that some or every x-thRI reporting instance is replaced with a PI. When a PI is fed back insuch a manner, future report types that are fed back may be for thattransmission point until another PI is fed back, for example.

Embodiments contemplate that the granularity of PMI and phase offset maybe reduced. For example, the phase offset may be jointly encoded withthe PMI of at least one of the transmission points. The PMI's may besubsampled such that certain PMI's may be associated with certain phaseoffset, and feeding back a specific PMI may, at least implicitly,indicate the transmission point a subset of possible phase offsets.Embodiments contemplate that another indicator may be used by thenetwork to determine the offset from the subset. For example, the phaseoffset may be fed back in the instance where another feedback reporttype may be scheduled. A flag may be transmitted by the WTRU indicatingthe report type that instance is being used for, for example.

Embodiments contemplate that for the modes where the WTRU may selectsubbands in some or each bandwidth part, the report type may include atleast one of the following:

-   -   for some points or for each point, the WTRU may select at least        one subband in some or every bandwidth part (where the set of        bandwidth parts may span the entire bandwidth). Therefore, for        some points of for each point the WTRU may have a different set        of subbands;    -   for some points or for all points, the WTRU may select one        subband in some or every bandwidth part. Therefore, the same set        of subbands may apply to some points or to all points;    -   in some or every bandwidth part, the WTRU may select at least        one subband/point combination. In this case, the WTRU may        provide a label that indicates both the subband within the        bandwidth part and the point for which it is applicable, for        example.    -   Embodiments contemplate that, whether the WTRU selects a common        set of subbands for all points, or a separate set of subbands        for each point, may be configured by higher layers. One or more        such configurations may be provided by the network, perhaps in        some embodiments according to the intended type of coordinated        transmission. For instance, the WTRU may be configured to select        a common set of subbands for some or all points, for example in        case the network intends to use joint transmission.        Alternatively or additionally, the WTRU may be configured to        select a separate set of subbands for some points or for each        point, for example in case the network intends to use dynamic        point selection.

The CSI that the WTRU reports periodically may be subject to at leastone associated condition as described herein, which may be determinedusing at least one of:

-   -   Higher-layer signaling, such as the configured reporting mode        and sub-mode; and/or    -   The last reported PTI, or the last reported type indication        (possibly newly defined).

In one or more embodiments, report types for multiple cells may becombined. A reporting mode may allow for the combination of report typesfor multiple cells. For example, multiple transmission points may usethe same rank. In this reporting mode, one RI may be sent for multipletransmission points. This reporting mode may configure the WTRU tofeedback (e.g., for n points) 1 RI, n wideband CQI, n wideband PMI and,if configured, multiple sub-band CQI and PMI, for example.

Embodiments contemplate examples of periodic CSI reporting according toan existing or previously undefined reporting mode. For example, in atleast one reporting mode/sub-mode, the WTRU may report the following:

-   -   in a first set of reporting instances separated by a first        period, a report type containing a common (or joint) rank        indicator;    -   in a second set of reporting instances separated by a second        period (excluding those reporting instances belonging to the        first set), a report type containing at least one wideband        aggregated (or joint) CQI and at least one wideband combining        indicator i_(comb); and/or    -   in a third set of reporting instances separated by a third        period (excluding those reporting instances belong to the first        or second sets), a report type containing at least one sub-band        aggregated (or joint) CQI and at least one sub-band combining        indicator i_(comb).        Embodiments contemplate that the reporting modes described may        be useful in combination with periodic reporting that may be        separately configured for some transmission points or each        transmission point.

Also by way of example, in at least one reporting mode/sub-mode, theWTRU may report the following:

-   -   in a first set of reporting instances separated by a first        period, a report type containing a common (or joint) rank        indicator, one per-point rank indicator for at least one        transmission point and a precoding type indicator (PTI) which        the WTRU may determine according to techniques described herein;    -   in a second set of reporting instances separated by a second        period (excluding those reporting instances belonging to the        first set), a report type containing:        -   in case the latest PTI transmitted by the WTRU was set to a            first value, one long-term (first) per-point precoding            matrix indicator and possibly one per-point long-term            combining indicator i_(1k,comb) for some or each            transmission point (possibly in different reporting            instances—in some embodiments);        -   in case the latest PTI transmitted by the WTRU was set to a            second value, at least one wideband aggregated (or joint)            CQI and one wideband short-term (second) per-point precoding            matrix indicator and one per-point (short-term) wideband            combining indicator i_(2kcomb) for some or each transmission            point (possibly in different reporting instances); and/or    -   in a third set of reporting instances separated by a third        period (excluding those reporting instances belonging to the        first set or the second set), a report type including:        -   in case the latest PTI transmitted by the WTRU was set to a            first value, at least one wideband aggregated (or joint) CQI            and/or at least one wideband short-term (second) per-point            precoding matrix indicator and/or at least one per-point            (short-term) wideband combining indicator i_(2kcomb) for            some or each transmission point (possibly in different            reporting instances); and/or        -   in case the latest PTI transmitted by the WTRU was set to a            second value, at least one sub-band aggregated (or joint)            CQI and/or at least one sub-band short-term (second)            precoding matrix indicator and/or at least one (short-term)            sub-band combining indicator i_(2kcomb) for some or each            transmission point (possibly in different reporting            instances).

In one or more of the previously described exemplary sub-bands, the WTRUmay set the precoding type indicator to the first value when, forinstance, the WTRU may determine that the long-term per-point precodingmatrix indicator and/or long-term per-point combining indicator may havechanged significantly for at least one transmission point since theprevious transmission of the precoding type indicator set to the firstvalue. Alternatively, the WTRU may set the precoding type indicator tothe first value periodically some or every N sub-frames or reportinginstances in order to prevent error propagation, for example. In one ormore embodiments, the value of N may be configured by higher layersignaling, for example.

One or more embodiments contemplate the reporting mode/sub-mode, such asfor example, where the WTRU may report the following:

-   -   in a first set of reporting instances separated by a first        period, a report type containing a common (or joint) rank        indicator, a precoding type indicator (PTI) and a joint        precoding type indicator (JPTI) which the WTRU may determine        according to at least one of the following:        -   the WTRU sets JPTI to a first value if different layers are            to be transmitted from different transmission points            (combining matrix is identity matrix); and/or        -   the WTRU sets JPTI to a second value if at least one layer            is to be transmitted from different transmission points;    -   in a second set of reporting instances separated by a second        period (perhaps excluding those reporting instances belonging to        the first set), a report type containing at least one of:        -   in case the latest PTI transmitted by the WTRU was set to a            first value, one long-term (first) per-point precoding            matrix indicator for each transmission point (possibly in            different reporting instances); and/or        -   in case the latest PTI transmitted by the WTRU was set to a            second value, at least one wideband aggregated (or joint)            CQI and/or one wideband short-term (second) per-point            precoding matrix indicator for some or each transmission            point (possibly in different reporting instances—in some            embodiments) and, in case the latest JPTI reported by the            WTRU was set to a second value, one wideband combining            indicator i_(comb); and/or    -   in a third set of reporting instances separated by a third        period (perhaps excluding those reporting instances belonging to        the first set or the second set), a report type containing:        -   in case the latest PTI transmitted by the WTRU was set to a            second value, at least one wideband aggregated (or joint)            CQI and/or one wideband short-term (second) per-point            precoding matrix indicator for some or each transmission            point (possibly in different reporting instances—in some            embodiments) and, in case the latest JPTI reported by the            WTRU was set to a second value, one wideband combining            indicator i_(comb).

In case the latest PTI transmitted by the WTRU was set to a secondvalue, at least one sub-band aggregated (or joint) CQI and/or onesub-band short-term (second) per-point precoding matrix indicator forsome or each transmission point (possibly in different reportinginstances) and, in case the latest JPTI reported by the WTRU was set toa second value, one sub-band combining indicator i_(comb).

Embodiments contemplate one or more techniques in which periodicfeedback may be based on independent periods and/or offsets. Statedsomewhat differently, embodiments contemplate realizing periodic CSIfeedback that may be based on transmitting periodic CSI reports inmultiple sets of subframes, where some or each of which may be definedby at least a period and/or an offset. In such embodiments, the CSIreports that may be transmitted in a specific set of subframes maypertain to at least one of:

-   -   A transmission point, or set of transmission points, or set of        CSI-RS-resources;    -   A CSI process;    -   A transmission state (for instance, the report for a Joint        Transmission or for a single point transmission);    -   An associated condition; and/or    -   A report type (for instance, whether the WTRU may report Rank        Indication or CQI/PMI feedback).        Embodiments contemplate that the period and/or offset of a given        set of subframes may be derived from parameters indicated by        higher layers, for example.

In one or more embodiments, the WTRU may transmit the CSI reports forsome combinations of report types and transmission points or, in someembodiments every possible combination of report type and transmissionpoint, each in a different set of subframes. For instance, the WTRU maytransmit RI of point 1 in subframe set A, RI of point 2 in subframe setB, CQI/PMI of point 1 in subframe set C, CQI/PMI of point 2 in subframeset D, etc.

In one or more embodiments, the WTRU may transmit the CSI reports for acertain type of feedback that may be applicable to some or alltransmission points in a single set of subframes. This may be useful fora number of reasons, such as for example in case some types of CSIinformation are common between transmission points. For instance, the RImay be common to some or all CSI processes, transmission points, thetransmission state, and/or may be linked to the RI for a specific CSIprocess or transmission point. For instance, the WTRU may be configuredsuch that the reported RI for a first CSI process may be constrained tobe the same as the reported RI for a second CSI process, where in someembodiments the second CSI process may be referred to as a “RI-referenceprocess” of the first CSI process. In such scenarios, the informationmay be transmitted in a single set of subframes instead of one set ofsubframes per transmission point or CSI process, perhaps savingoverhead. In some embodiments, this may be realized, for instance, ifthe configured reporting instances for the rank indication may be thesame for both processes. In such scenarios, the RI report of the firstCSI process may be dropped according to a priority rule, such that theRI applicable to both processes may be reported in a single set ofreporting instances. The same technique may be applied to a transmissionstate indicator (TSI), or to a PI indicating an ordered set oftransmission points, for example.

In one or more embodiments, a given set of subframes may be linked to aspecific set of transmission points (or CSI-RS-resource), ortransmission state (such as a joint transmission) or CSI process on asemi-static basis. To minimize overhead, the WTRU may determine that acertain type of CSI associated to a certain transmission point ortransmission state or CSI process may be transmitted if a certaincondition or conditions are satisfied, and in some embodiments perhapsonly if a certain condition or conditions are satisfied. For instance, acondition may be associated to the transmission state or CSI processthat the WTRU may determine. The WTRU may transmit CSI feedback for acertain transmission point if this transmission point may be involved ina transmission to the WTRU according to the determined transmissionstate or CSI process, and in some embodiments perhaps only if thistransmission point may be involved in a transmission to the WTRUaccording to the determined transmission state or CSI process. Also byway of example, another condition may be that a metric associated to thetransmission point or state (such as the wideband CQI) may be betterthan the metric associated to the best transmission point or state minusa threshold. In case the WTRU may determine that a certain transmissionpoint or transmission state or CSI process does not satisfy thecondition for transmission, the WTRU may indicate this to the network ina separate type of report, such as a TSI or a heretofore undefined typeof report, possibly in a separate set of subframes that may be specificto the transmission point, for example. In one or more embodiments, thetransmission of CSI feedback for a certain transmission point or pointsmay be conditioned to the latest transmitted value of this report, forexample.

In one or more embodiments, the linkage between a set of subframes and atransmission point may be dynamic. For instance, transmission points maybe ranked by the WTRU using at least one quality criterion (such ashighest RI or highest wideband CQI, for example). The WTRU may indicatethis ranking in a heretofore undefined report type containing PI and maybe transmitted in a specific set of subframes. Based on the latesttransmitted PI, the CSI for the highest ranked transmission point maythen be transmitted in a first set of subframes, the CSI for the secondhighest in a second set of subframes, and so on. This technique mayallow for the transmission of feedback for more important transmissionpoints more frequently than for less important points, for example.

Embodiments contemplate that a report type may be fed back where theWTRU may provide the new ranking of the transmission points. Theperiodicity/offsets of each transmission point may be pre-configuredand/or tied to the rank provided by the WTRU. In one or moreembodiments, the WTRU may send at least two lists, one with “good”transmission points that may require the higher periodicity, and anotherwith “bad” transmission points that may require lower periodicity. Thenumber of lists may grow with the required periodicity granularity, forexample. The WTRU may also report the PI containing the list of pointsusing higher layer signaling.

When a WTRU may be configured to feedback CSI for a number oftransmission points or CSI cases using one of the aforementionedtechniques, a collision of feedback reports may occur if there isoverlap between sets of subframes. In one or more embodiments, an orderof precedence of transmission points (or CSI cases) may bepre-configured by the network, such as for example in case the collisionoccurs for the same report type, and in some embodiments may bepre-configured only in case the collision occurs for the same reporttype. In such embodiments, perhaps if two transmission points (or CSIcases) have feedback reports scheduled for the same resources, the WTRUmay feedback the report for the transmission point (or CSI case) havinghigher precedence. In one or more embodiments, the WTRU may select whichtransmission point (or CSI case) to feedback. The feedback CSI mayinclude a PI or TSI to indicate which point of CSI case or CSI processthe feedback is for, for example.

Embodiments contemplate that periodic feedback collisions of feedbackreports may be predicted by the network when configuring the reportingof some or each CSI case. Embodiments contemplate that the network mayreconfigure the reporting modes and/or reporting instances to perhapsensure there may be no collision for a network-selected period of time.Alternatively or additionally, the network may configure the WTRU withfeedback reports such that there may be collisions of feedback reportsin specific instances. In order to deal with such situations, amongother reasons, the WTRU may be configured with rules to compress,juxtapose, and/or drop some feedback reports.

Embodiments contemplate that one or more techniques regarding collisionof feedback reports. Embodiments contemplate that some or any WTRUconfiguration may be static (for example, the WTRU behavior when acollision occurs may be included in a SIB), semi-static (and updated viahigher layer signaling), or dynamic (and updated either by higher layersignaling or by an element in a DCI), for example.

Embodiments contemplate that at least two types of feedback reportcollision may occur. In a first type, the two feedback reports collidingmay be for different feedback types. For example, there may be acollision of a RI report for a first CSI case or CSI process feedbackand of a wideband CQI/PMI of a second CSI case or CSI process feedback.In collision cases where the two feedback reports are of different type,the WTRU may use any one or more of the following techniques:

-   -   There may be a hierarchy of feedback reports. In one or more        embodiments, the WTRU may drop certain report types in favor of        others. A list of priorities may be configured to the WTRU. For        example, a first priority report types may include: Wideband        First PMI (2a), RI (3), Wideband CQI (4) and RI/PTI (6). A        second priority report types may include: Wideband CQI/PMI (2),        Wideband CQI/Second PMI (2b), Wideband CQI/First PMI/Second PMI        (2c), RI/First PMI (5). Third priority report types include:        Sub-band CQI (1), Sub-band CQI/Second PMI (1a). Also by way of        example, some or all the feedback report types may have the same        priority;    -   Certain components of CSI cases or CSI processes (such as the        desired signal or interference component) may be configured with        priority. In one or more embodiments, perhaps in the event of a        collision, the WTRU may feed back the report type for the CSI        case or CSI process whose components have higher priority and        drops others;    -   The priority of CSI cases or CSI processes may be determined by        ranking higher or lower, the CSI cases or CSI processes by those        that share desired signal (or interference component). For        example, if there are three CSI cases or CSI processes and two        share the same desired signal, in one or more embodiments, they        may be of higher (or lower) priority than the third CSI case or        CSI process which may have a different desired signal;    -   There may be a hierarchy of feedback modes and the WTRU may        select to feed back report types which are generated for higher        priority feedback modes while dropping reports of lower priority        modes in one or more embodiments;    -   Feedback for wideband reports may be considered higher or lower        priority than feedback for subband reports in one or more        embodiments;    -   Feedback for per-point CSI cases or CSI processes (e.g., with a        single CSI-RS resource assumed as desired signal) may be        considered higher or lower priority than feedback for aggregated        CSI cases or CSI processes in one or more embodiments;    -   A CSI case's or CSI process' feedbacks may not be dropped more        than a configured number of times in a row in one or more        embodiments. In such embodiments, perhaps when a collision of a        same priority occurs, if a CSI case's or CSI process' feedbacks        have been dropped the configured amount of times in a row, it        may have a priority and the WTRU may feedback reports associated        to the CSI case or CSI process. The “drop” counter may then be        reset to 0; and/or    -   Based on a previous feedback report type (a new indicator        similar to PTI), the WTRU may feedback a specific report type        and drop another in one or more embodiments.

One or more embodiments contemplate that, perhaps in the event of acollision between two report types of the same priority, the WTRU may beconfigured to keep the feedback report for a pre-determined CSI case orCSI process (and in some embodiments perhaps only such a feedbackreport). Alternatively or additionally, the WTRU may be configured tofeedback the report type for a CSI case or CSI process, or a subset ofCSI cases or CSI processes (and hence drop some or all other collidingfeedback reports from other CSI cases or CSI processes) that may beselected based on a configured criterion such as any combination of:

-   -   Order of the CSI case or CSI process in the configuration, for        example as indicated by a CSI process identifier;    -   Measurement metric (e.g. CSI-RSRP) of the CSI-RS resource        assumed as desired signal in the CSI case or CSI process;    -   Measurement metric of the CSI-RS resource assumed as interfering        signal in the CSI case or CSI process;    -   Interference level measured from an interference measurement        resource in the CSI case or CSI process;    -   Explicit priority of the CSI case or CSI process provided as        part of the configuration, for example, as indicated by a CSI        process identifier where a lower value may have a higher        priority;    -   Number of CSI-RS resources assumed as interference in the CSI        case or CSI process (for instance, a higher priority may be        assigned to a CSI case or CSI process that has a larger number        of CSI-RS resources assumed as interference);    -   CSI case(s) or CSI processes with highest or lowest CQI;    -   CSI case(s) or CSI processes with highest or lowest RI;    -   CSI case(s) or CSI processes with highest or lowest desired        signal strength;    -   CSI case(s) or CSI processes with highest or lowest interference        signal strength;    -   CSI case(s) or CSI processes with highest or lowest feedback        reporting periodicity;    -   CSI case(s) or CSI processes with most or least recently dropped        feedback report;    -   CSI case(s) or CSI processes whose previous feedback with the        same report type was most or least recently fed back;    -   Next CSI case(s) or CSI processes based on a preconfigured        cycling of CSI cases or CSI process;    -   CSI case(s) or CSI processes whose colliding feedback report may        have changed the most or the least since the WTRU last        successfully fed back that report type for that CSI case or CSI        process. For example, if the two colliding feedback report types        are RI from CSI case or CSI process A and PMI from CSI case or        CSI process B and the value of RI has not changed since the last        successful feedback of RI for CSI case or CSI process A, then        the WTRU may select to feedback the PMI feedback report type for        CSI case or CSI process B;    -   CSI case(s) or CSI processes that was included in the most        recent aperiodic feedback report instance;    -   Duration since the last time CSI was reported for a CSI case or        CSI process in an aperiodic report, a periodic report or any        report; and/or    -   CSI case or CSI process whose CSI-RS resource assumed as a        desired signal may be transmitted from a point that was last        used for a downlink assignment.

Embodiments contemplate that the aforementioned criteria may have lower(or higher) precedence than existing criteria used for prioritizationpurposes based on a report type of serving cell. For instance, the“report type” criterion may have higher precedence than one of the above“CSI case” or “CSI process” criterion such that in case of a collisionbetween CSI reports of different types (e.g. rank indicator vs.pre-coding matrix indicator) and/or of different CSI cases or CSIprocesses, the priority may be set first according to the report typeirrespective of the priorities of the CSI cases or CSI processes. Inanother example, the “serving cell” criterion may have higher (or lower)precedence than one of the above “CSI case” or “CSI Process” criterionsuch that in case of a collision between CSI reports for differentserving cells and/or for different CSI cases or CSI processes, thepriority may be set first according to the serving cell (or firstaccording to the CSI process). In some embodiments, perhaps if thepriority between CSI processes of a serving cell may be set according toa lower CSI process identifier first, and/or the priority between CSI ofdifferent serving cells may be set according to a lower serving cellidentifier first, the priority rule in case of collision between CSIprocesses with different CSI process identifiers and from differentserving cells may be according to the CSI process identifier. In suchscenarios, one or more, or all, CSI reports except the CSI report fromthe serving cell with the CSI process that may have the lowest CSIprocess identifier may be dropped.

In one or more embodiments, the select report type and CSI case or CSIprocess that are fed back may not be obvious to the network. In suchscenarios the WTRU may add a CSI case or CSI process indicator (such asa PI or TSI) to inform (and perhaps to explicitly inform) the network ofwhat report was fed back.

Alternatively or additionally, the WTRU may be able to compress thefeedback reports in order to combine the colliding reports into one. Insuch embodiments, the WTRU may, in the event of a collision, reportdifferential values for the feedback reports (and in some embodimentsperhaps only such differential values). These differential values may bedone with respect to the most recent successful feedback report of eachcolliding type and for the respective CSI cases or CSI processes, forexample.

Alternatively or additionally, the WTRU may be configured such that inthe case of a collision, it may transmit the feedback using a channelwith a larger available payload (such as use PUCCH Format 3) in aseparately configured resource. Further, in some embodiments, the WTRUmay be configured to use such resource in the case of a collision of nfeedback reports (and in some embodiments perhaps only in such a case),where n may be any integer equal to or greater than 2, for example.

Embodiments contemplate that another type of collision may occur wherethe two or more colliding feedback reports may be of the same type butfor different CSI cases or CSI processes. In such embodiments, the WTRUmay re-use any of the techniques described herein for the case ofdifferent feedback types colliding, and/or any combination of thefollowing:

-   -   In one or more embodiments, the WTRU may feedback a single        report that may be interpreted as the value to be used for some        or all the colliding reports, at the network. For example, the        WTRU may be configured such that some or any CSI cases with a        same desired signal component (or same interference component)        may share certain feedback report types, such as RI and/or CQI        and/or PMI. The sharing rules may be different based on whether        the desired signal or interference components are the same, for        example;    -   In one or more embodiments, the WTRU may be configured such that        whenever there may be a collision of same feedback types, the        WTRU may determine a single value of this feedback type that may        be most appropriate for some or all colliding CSI cases or CSI        processes (and in some embodiments must so determine);    -   In one or more embodiments, the WTRU may be configured with        groups of CSI cases or CSI processes who may share certain        feedback types as well as what feedback type may be shared. In        the case of collision of these pairs of types and CSI cases or        CSI processes, the WTRU may feedback a single value;    -   In one or more embodiments, the WTRU may feedback an absolute        value of the report type for one CSI case or CSI processes and        differential values for some or all other colliding CSI cases or        CSI processes. The selection of what point to feed back the        absolute value can be done similar to the criteria described        herein for collision of different feedback types. One or more        such embodiments may be used if the colliding CSI case or CSI        process has the same subset of CSI-RS resources assumed as        interference, or if it may be indicated by higher layers that        differential reporting is used (and some embodiments may be used        perhaps only in such conditions);    -   The WTRU may be configured with sub-sampled codebooks from which        to select PMI in the event of collision of feedback reports. The        sub-sampled codebooks may be pre-configured, tied to feedback        instances, and/or may be dynamically switched from sets of        codebooks pre-configured. The dynamic switching may be done by        indication in the aperiodic grant, or it may be cycled through a        pre-configured set, or may be selected by the WTRU and indicated        with a new indication bit(s), for example; and/or    -   The WTRU may add an indication bit(s) to indicate whether the        feedback report is valid for some or all colliding CSI cases or        CSI processes, a single CSI case or CSI process, and/or a subset        of colliding CSI cases or CSI process.

Embodiments contemplate that periodic feedback may be based ontransmission of reports for multiple points. For various reasons, suchas to perform periodic CSI reporting, for example, the WTRU may beconfigured with any of the available Rel-10 reporting modes for singlepoint feedback. Embodiments contemplate that the modes may be augmentedby including a heretofore undefined Report Type to include the TSIand/or PI. The contemplated report type may be a heretofore undefinedstandalone report type or may be jointly provided with any other reporttypes (for example a report type combining RI with TSI). In such a case,some or all other feedback report types may be conditioned on point(s)indicated in the most recently transmitted report type that includes TSIand/or PI. In one or more embodiments, the TSI may be transmitted withhigher periodicity than the PI or any other report type and the PI maybe transmitted to indicate for which point in the TSV (indicated by TSI)the future reports may be conditioned on. Alternatively or additionally,some or all feedback reports may include TSI and/or PI that may indicatefor what point that specific report is for.

In one or more embodiments, CSI components pertaining to more than onepoint may be reported in the same subframe. For instance, it may bepossible to maintain, modify or expand existing report types (such as 1,1a, 2, 2a, 2b, etc., for example) such that the type of CSI informationprovided in these reports may be provided for multiple points instead ofa single point. Embodiments contemplate that his may result inincreasing the information payload of some reports or each report, butalso may facilitate the maintenance of the time organization of existingperiodic modes regardless of the number of transmission points, forexample.

Embodiments contemplate one or more techniques that may be applicable toone or more specific report types such as but not limited to:

-   -   In reports 1 and 1a which may contain sub-band CQI information        for the best WTRU-selected sub-band of a BW part, the WTRU may        report a sub-band for both points (and perhaps a single sub-band        for both points), or one sub-band for each point;    -   In reports which may contain CQI (1, 1a, 2, 2b, 2c, 4, for        example), the WTRU may report at least one of the following        (wherein it is contemplate that per-point CQI may be with or        without muting hypothesis):        -   Per-point CQI for the first codeword of each point, spatial            differential per-point CQI for the second codeword of each            point (if RI>1), some or each of which may be relative to            the first codeword of the respective point;        -   Per-point CQI for the first codeword of one point,            differential per-point CQI for the first codeword of each            other point (some or each of which may be relative to the            first codeword of the first point), differential per-point            CQI for the second codeword of each point (if RI>1, for            example), some or each of which may be relative to either            the first codeword of the first point, or the first codeword            of the respective point; and/or        -   Aggregated CQI for the first codeword assuming joint            transmission from some or all points, spatial differential            aggregated CQI for the second codeword (if RI>1, for            example) assuming joint transmission from some or all            points;    -   In reports which may contain PMI or second PMI (1a, 2, 2b, 5,        for example):        -   Per-point PMI for some or each point with less than 8            antenna ports, second PMI for some or each point with 8            antenna ports;        -   For some or each point other than the first, at least one            phase offset between first point and this point; and/or        -   One or more combining indicator (for example, a single            indicator that may be pointing to a co-phasing matrix            between points); and/or    -   In case at least one point may have 8 antenna ports:        -   Reports 2a or 2c may contain first PMI for the points that            have 8 antenna ports, and in some embodiments reports 2a or            2c may only contain first PMI for the points that have 8            antenna ports

In one or more embodiments, the contemplated report type that includesthe TSI may also include an order of points for which CSI may be fedback (for example a vector of points). In such a case, feedback reportsoccurring after the TSI and the order of points have been fed back maybe for the first point. A heretofore undefined single bit flag may beadded to any of the contemplated report types such that upon feedingback a predefined value for the flag, the point on which future reportsmay be conditioned cycles to the next point in the vector of orderedpoints. Alternatively or additionally, in one or more embodiments, theorder of points may be signaled by the network to the WTRU.

In one or more embodiments, the WTRU may be configured in a Rel-10periodic feedback mode. Embodiments contemplate that the WTRU may beconfigured with a period and/or an offset that may associate a subframenumber with a point and/or TSI and/or PI. Some or all feedback reportsmay be conditioned on the point to which the subframe is associated, andin some embodiments, some or all feedback reports must be conditioned onthe point to which the subframe is associated.

In one or more embodiments, the report type including the TSI, and/or PIor higher layer signaling, or the subframe number may also, eitherexplicitly or implicitly include information on whether feedback reportsare for aggregated or per-point values. Aggregated feedback may beaccomplished by removing the conditioning of report types on the PI mostrecently reported and/or by conditioning some or all aggregated reporttypes on the most recently fed back TSI. Alternatively or additionally,the aggregated feedback may be accomplished by transmitting adifferential value that may be conditioned on a preselected point'sfeedback. The preselected point may be determined by a metric such as,but not limited to, a highest per-point CQI. For example, point 1 may beconsidered the reference point; therefore when the PI indicates point 1feedback, the CQI may represent per-point CQI of point 1. In one or moreembodiments, when the PI indicates other points, the CQI may representthe differential value (compared to point 1 per-point CQI) to providethe aggregated CQI, for example.

Embodiments contemplate periodic feedback that may be based on cyclingbetween transmission points and/or states. In one or more embodiments,the WTRU may be configured with one of the Rel-10 reporting modesaugmented by allowing certain feedback report types to cycle through thepoints. For example, in the case where RI is configured, the WTRU mayfeedback at least one value for some or all points (i.e. an aggregateRI), and in some embodiments perhaps only one value for some or allpoints. In one or more embodiments, some or each successive RI reportmay represent the rank of a different point. The point upon which an RIreport may be configured can be obtained by cycling through a vector ofpoints. The vector of points may be implicitly determined from the mostrecent TSI and/or PI, or may be explicitly fed back by the WTRU in aheretofore undefined report type, or may be preconfigured by the networkvia higher layer signaling, for example. In one or more embodiments,when the WTRU uses RI cycling, the RI reporting per-point period maybecome N_(points)*M_(RI)*N_(pd) (where N_(points) is the total number ofpoints and the reporting interval of RI reports is an integer multiple(M_(RI)) of the CQI/PMI report period N_(pd) as defined in, for example,3GPP TS 36.213.

In the case where wideband CQI/PMI reporting may be configured, the WTRUmay cycle through some points or each point for each successivereporting on CQI/PMI. In such a case, the periodicity with which some oreach point's CQI/PMI is reported may be given by N_(points)*N_(pd).Embodiments contemplate that where the PMI may be indicated in two parts(e.g., PMI1 and PMI2), the cycling of points for each precoding matrixmay be dependent or independent. For example, in single-point reportingMode 2-1, if PTI=0, the following order of reports may be configured:

W-PMI1, W-CQI/W-PMI2, W-CQI/W-PMI2 W-CQI/W-PMI2, W-PMI1, W-CQI/W-PMI2,W-CQI/W-PMI2, W-CQI/W-PMI2 . . . .

(where W means wideband, PMI1 means the first precoder matrix indicatorand PMI2 means the second precoding matrix indicator). When cyclingthrough points, the following example demonstrates that the cycling ofW-PMI1 and W-PMI2 may be dependent:

W-PMI1_(a), W-CQI/W-PMI_(2a), W-CQI/W-PMI_(2a) W-CQI/W-PMI_(2a),W-PMI1_(b), W-CQI/W-PMI_(2b), W-CQI/W-PMI_(2b), W-CQI/W-PMI_(2b) . . . .

In one or more dependent methods, embodiments contemplate that cyclingmay occur for one report type (for example the PMI1), and in someembodiments perhaps only one report type, and the other report type maybe conditioned on the point used for the cycled report type.Alternatively, embodiments contemplate that the cycling may beindependent:

W-PMI1_(a), W-CQI/W-PMI_(2a), W-CQI/W-PMI_(2b) W-CQI/W-PMI_(2c),W-PMI1_(b), W-CQI/W-PMI_(2a), W-CQI/W-PMI_(2b), W-CQI/W-PMI_(2e) . . . .

(Where the lettered subscript is used to denote different points).

Embodiments contemplate that the concept of dependent and independentcycling may be attributed to any of the report types. For dependentcycling, in some embodiments, one report type may be considered theanchor upon which another report type's point dependence may beconditioned. For example, for the case where both wideband CQI/PMI andsubband CQI are configured, if the subband CQI is anchored to thewideband CQI then the point upon which a subband report may beconditioned on may depend on the point for the most recent wideband CQI.As an illustrative example, in mode 2-0, for single point and twobandwidth parts, the reporting may be:

W-CQI, S-CQI₁, S-CQI₂, S-CQI₁, S-CQI₂, W-CQI, S-CQI₁, S-CQI₂, S-CQI₁,S-CQI₂ . . . .

(where the numbered subscript indicates a subband number).

Embodiments contemplate that when cycling through points, the followingshows an example of cycling dependence between subband CQI and widebandCQI:

W-CQI_(a), S-CQI_(1,a), S-CQI_(2,a), S-CQI_(1,a), S-CQI_(2,a), W-CQIb,S-CQI_(1,b), S-CQI_(2,b), S-CQI_(1,b), S-CQI_(2,b) . . . .

In such a case, the periodicity of the wideband CQI may be given byN_(points)*H*N_(pd) (where H is an integer multiple used to determinethe periodicity of wideband CQI/wideband PMI reporting as defined in,for example, 3GPP TS 36.213.

For one or more embodiments, the following shows an example of cyclingindependence between wideband CQI and subband CQI:

W-CQI_(a), S-CQI_(1,a), S-CQI_(2,a), S-CQI_(1,b), S-CQI_(2,b),W-CQI_(b), S-CQI_(1,a), S-CQI_(2,a), S-CQI_(1,b), S-CQI_(2,b) . . . .

One or more embodiments contemplate that subband reporting may cyclethrough some or all the bandwidth parts of at least one point insuccessive reports before cycling through the points. Alternatively oradditionally, the order of cycling can be reversed such that insuccessive reports some or all the subband reports for different pointsmay be cycled through while keeping the bandwidth part constant, beforecycling through the bandwidth parts. Embodiments contemplate thatcycling and/or dependency of cycling may be applicable to anycombination of report types and for any report mode. In one or moreembodiments, the cycling may be done over some or all the points andalso over the two hypotheses of aggregated or per-point feedback.

Embodiments contemplate techniques for the reporting of channel stateinformation from multiple transmission points using measurement reportsgenerated at the RRC layer. In one or more embodiments, a WTRU mayestimate a received signal strength (RSRP) and/or quality (RSRQ) and/orpathloss of a subset of transmission points of a certain cell based onmeasuring the CSI-RS reference signal(s) transmitted for a subset oftransmission points.

Embodiments also contemplate that a WTRU may estimate a received signalstrength (RSRP) and/or quality (RSRQ) and/or pathloss of a subset oftransmission points of a certain cell based on measuring a previouslyundefined type of reference signal(s) (that may be called transmissionpoint reference signal or TP-RS) transmitted for this subset oftransmission points. The TP-RS may be transmitted for and may bereceived by the CoMP-capable WTRU according to this method duringspecific subframes, and in some embodiments perhaps only during specificsubframes, which may be defined as “multi-port measurement” sub-frame,and whose pattern may be provided by higher layers. Such sub-frames maybe included as a subset of MBSFN-subframes to prevent legacy WTRU's fromattempting to perform certain measurements and related processing inthese subframes, for example.

Embodiments contemplate that the TP-RS transmitted from different(neighboring) transmission points may be transmitted in different OFDMsymbols to prevent loss of accuracy due to potential power imbalancebetween the signals received from these points.

Using CSI-RS or TP-RS for its measurements, the WTRU may then separatelyreport RSRP or RSRQ values of some or each transmission point of a sameand/or different cell(s). Based on the RRC measurement reports thenetwork may explicitly configure the WTRU with the subset oftransmission points for CSI reporting. Embodiments contemplate that thehigher layer RSRP measurements per CSI-RS or per TP-RS may be used bythe network to manage the set of CSI-RS resources that the WTRU may usefor the purpose of CSI measurement reporting, among other reasons, forexample.

More specifically, the WTRU, perhaps as part of the measurementconfiguration, may be configured with a list of transmission points,CSI-RS or TP-RS (ports) to measure. The configuration may include atleast one subset of CSI-RS or TP-RS configuration, which may correspondto one or a combination of the following: a list of CSI-RS or TP-RSrelated to the serving cell (e.g. CSI-RS or TP-RS transmitted from theWTRU's serving cell, primary serving cell, or alternatively secondarycell); a list of CSI-RS or TP-RS associated to a particular PCI; and/ora list of CSI-RS or TP-RS that may be associated to any PCI.

Embodiments contemplate that a configuration of a CSI-RS or TP-RS thatmay be used for higher layer measurements may include at least one ofthe following configuration parameters:

-   -   Antenna port count (e.g. 1, 2, 4, or 8);    -   Resource config (e.g. resource element configuration of the        CSI-RS or TP-RS);    -   Subframe config (e.g. subframe in which the CSI-RS or TP-RS is        transmitted);    -   Assumed ratio of PDSCH EPRE to CSI-RS EPRE (e.g. Pc value);    -   At least one parameter used for the derivation of an initial        value of the pseudo-random sequence for the CSI-RS, such as a        virtual cell identity. In one or more embodiments, some or each        port or subset of ports may have its own pseudo-random sequence        initialization configuration; and/or    -   Associated PCI—this parameter may be included if the CSI-RS or        TP-RS corresponds to a cell different than the serving cell or        Pcell. Additionally, this parameter may be included if CSI-RS of        different cells may be configured for RSRP measurements.        In one or more embodiments, the network may configure a full or        partial set of parameters described above for some or every        CSI-RS included for the higher layer measurement set in the        WTRU, for example.

Alternatively or additionally, one or more embodiments contemplate thatfor a number of reasons, such as to optimize signaling for example, asubset of the previously described configuration may be common acrossthe configured transmission points (e.g. one parameter may be providedfor some or all transmission points). The remaining subset may beprovided to the WTRU individually for some or each transmission pointconfiguration. For example, the antenna port count may be a commonparameter and the resource configuration, subframe configuration, and/orpseudo-random sequence configuration may be different for some or eachprovided transmission point (CSI-RS or TP-RS).

In another example, the subframe configuration may also be a commonconfiguration parameter across the transmission points configured forhigher layer measurements. More specifically, in such an example, theWTRU measurement set configuration may include one subframeconfiguration and potentially one antenna port configuration (oralternatively, a default antenna port configuration (e.g. 2) may beassumed) followed by a list of independent transmission point (e.g.CSI-RS or TP-RS) parameter configuration, which may include but are notlimited to, resource configuration and/or pseudo-random sequenceconfiguration.

By way of further example, one CSI-RS or TP-RS configuration may havemultiple subset of ports each with individual sequence generation. Thismay enable network flexibility in order to manage different CSI-RSconfigurations for different WTRUs. In this case, the WTRU may beinformed of the multiple sequence initiators as well as the ports forwhich some or each initialization may be applicable. Alternatively oradditionally, the WTRU may blindly decode and/or may attempt to measurethe RSRP of a CSI-RS transmitted (and detected) in a configured cell. Toassist the WTRU to blindly decode the CSI-RS or TP-RS, the WTRU may beprovided with a subframe configuration to search for CSI-RS given adefault antenna port count (e.g. 2 antenna port configuration) or agiven configured antenna port count. Additionally or alternatively,embodiments contemplate that the network may configure at least somesubframes to be used for blind decoding. In these subframes or any othersubframe, the same sequence generation initialization may be used forsome or all CSI-RS or TP-RS resources. The sequence generationinitialization may be obtained by the actual PCI of the macro cell, forexample.

Embodiments contemplate that the WTRU may go through some resourceelements or all possible resource elements in which CSI-RS for theantenna port count may be transmitted to detect potential transmissionsof CSI-RS. In one or more embodiments, when reporting the higher layermeasurement to the network, the WTRU may report along with the RSRP theResource element(s) in which the CSI-RS was detected. This may allow thenetwork to determine to which CSI-RS the measurement may correspondand/or to properly configure a CSI reporting set and/or a CoMP set. Inone or more embodiments, the WTRU may report along with the RSRP aresource configuration index (or resourceConfig parameter) that mayindicate the location of these resource elements. To further assist theWTRU in decoding the transmission points, in one or more embodiments,the network may provide a scrambling configuration for the CSI-RS pointsthat the WTRU may decode (or at least try to decode) in the configuredsubframe.

Alternatively or additionally, one or more embodiments contemplateCSI-RS whose sequences may be cyclic shifts of each other (e.g., nolonger a gold sequence, but more like a CAZAC sequence), in which caseno scrambling configuration may need to be provided to the WTRU inadvance. In such a case, some or all cooperating points may share thesame root sequence. One or more embodiments contemplate that the rootsequence may be conditioned on the subframe number in a manner that maybe preconfigured by the network and may be signaled to the WTRU viahigher layers, for example. Also, one or more embodiments contemplatethat for some or each transmission point, the WTRU may maintain and/ormeasure a measurement quantity which it may use for evaluation ofreporting criteria or for measurement criteria, for example.

By way of example, and not limitation, the measurement configurationmessage may provide the WTRU with one or a combination of information.For example, the information may include a set of measurement identitiesthat may be used for the purpose of multiple point transmission CSI-RSor TP-RS reporting (and in some embodiments perhaps only for the purposeof multiple point transmission CSI-RS or TP-RS reporting), that may ormay not belong to the serving cell physical identity. The informationmay include a set of measurement identities associated to at least onemeasurement object that the WTRU can use across some or all cells and/ortransmission points. Further, the information may include an indicationto configure the WTRU to measure the CSI-RS or TP-RS per transmissionpoint for the configured PCI (for example the serving cell). Thisconfiguration may be specific to a measurement identity or measurementobject or reporting configuration or, alternatively, may be appliedacross some or all measurement identities and/or events. In anotherexample, the information may include an indication to configure the WTRUto measure CRS as well, in addition to the list of CSI-RS or TP-RS. Inanother example, the WTRU may determine that it may measure, and perhapsin some embodiments may have to measure, different transmission pointbased on the presence of the list. The measurement identities for whichthese measurements may (and in some embodiments perhaps should) beperformed and for which the WTRU can use them for criteria evaluation,may be explicitly indicated in the measurement configuration message.Alternatively, the WTRU may apply them across some or all measurementidentities. In another example, the information may include an explicitindication to which measurement identity the measurements of thetransmission points within a subset can be applied to.

The range of measurement events and identities may vary across differentdeployment and networks, however, the WTRU may be configured with one ormore measurement events. For example, a measurement event may include anevent A4. In this example, the quality of a neighboring cell may becomebetter than a configured threshold for a configured period of time. Thisevent, when configured with an indication to measure the CSI-RS or TP-RSof multiple transmission points, may be interpreted by the WTRU, as thequality of a transmission point may become better than a configuredthreshold for a configured period of time. Additionally, the WTRU mayrestrict sending this event within transmission points in the servingcell, and in some embodiments perhaps only within transmission points inthe serving cell. In another example, a new or fresh event may bedefined to detect when the signal strength of a point may become betterthan the sum of an offset and of the worst signal strength of a set ofpoints (or equivalently when the signal strength of a point may becomebetter than the sum of an offset and of the signal strength of any of aset of points). In such an event, the set of points may be explicitlyconfigured by higher layers, or may correspond to the set of points in aCoMP measurement set. The set of points may be (re)configured with anyCoMP measurement set (re)configuration or may be (re)configuredindependently of the CoMP measurement set (re)configuration. In someembodiments, the offset may also be configured by higher layers and mayinclude a hysteresis value. Embodiments contemplate that such new orfresh events may be useful, for example to perhaps ensure that thenetwork may be notified whenever the CoMP measurement set may no longercontain the strongest points, or when the signal strength of a pointoutside of the CoMP measurement set may become greater than the signalstrength of some or any point within the CoMP measurement set, forexample.

In another example of a measurement event, the event may be when thequality of a transmission point of the serving cell may drop below aconfigured threshold. This may also be configured by setting“reportOnLeave” bit for event A4. In an example, the quality of atransmission point may become better than the quality of a transmissionpoint in the CSI reporting set or CoMP set by a threshold for aconfigured period of time. This may correspond to a previously undefinedevent that may be used for maintaining a CoMP set, for example.

Since the WTRU may be performing measurements for multiple transmissionpoints within the same cell or within different cells, for reasons suchas for example to allow for proper measurement criteria evaluation andcomparisons with other cells that may also be configured with multipletransmission points, the WTRU may use one or a combination of variousmeasurements. In an example, the WTRU, in addition to measuring theCSI-RS or TP-RS of some or all configured transmission points may alsoperform CRS measurements on the serving cell and/or neighboring cells,in some embodiments the CRS measurements may be R10 CRS measurements. Inthis example, a measurement may be used as a basis of comparison forother events. In another example, the WTRU may use the best measuredtransmission point for some cells or each cell as a reference forcomparison for other events (e.g., to evaluate and trigger event A3, theWTRU may take into account the quality of best transmission point withinthe serving cell, and in some embodiments may only take into account thequality of best transmission point within the serving cell). In anotherexample, the WTRU may use the first CSI-RS or TP-RS of some or eachconfigured subset, if configured. In another example, the WTRU may use afunction or an average of the CSI-RS or TP-RS measured from differentphysical channel identities or different subsets (e.g., alternatively,the CSI-RS or TP-RS used in the equation may be the CSI-RS or TP-RS inthe configured CoMP set (e.g. CSI report set)).

In another example, the WTRU may use some or all transmission pointmeasurements and may treat them as measurements from different cells.Then some or all configured events may be triggered for transmissionpoints within the same serving cell. For example, event A3 may betriggered when there may be a change of a best transmission point in aserving cell or when there may be a change of best cell when compared tosome or all transmission points in the serving cell. In another example,the WTRU may trigger the events if the transmission points for which thecriteria are met belong to the same subset (e.g., certain events may betriggered if the criteria are fulfilled for a transmission point). Inone or more embodiments, the WTRU may only trigger the events if thetransmission points for which the criteria are met belong to the samesubset (e.g., certain events may only be triggered if the criteria arefulfilled for a transmission point).

In one or more of the contemplated embodiments, the measurements takenon the CSI-RS or TP-RS may be used for evaluation of transmission pointspecific configured events and/or to perform transmission pointmeasurement quantity reporting. In such embodiments, neighboring cellsmeasurements performed on legacy CRS may be independently used for otherevent and/or reporting configurations. Embodiments contemplate that byway of a measurement configuration (e.g. measConfig), for example, theWTRU may be requested to perform intra-frequency measurements on a setof transmissions points on the serving cell and/or different cell(s). Inone or more embodiments, the WTRU may also be requested to performinter-frequency measurement of a set of transmission points on anotherfrequency.

In one or more embodiments, the WTRU may be configured with ameasurement object and/or reporting configuration that may, perhapsexplicitly, indicate to the WTRU that the configured event orconfiguration may be applied for CSI-RS or TP-RS measurements. This maybe performed using one or a combination of the following:

-   -   A new measurement object may be defined for transmission point        measurements on a CSI-RS or TP-RS. In one or more embodiments,        more than one measurement object for a frequency may be defined        (e.g. one measurement object for cell evaluation and one        measurement object for transmission point evaluation). The        report configuration may contain a new CoMP set management event        or an existing event configuration. Embodiments contemplate at        least one measurement identity may be configured to have an        associated measurement object that may contain a transmission        point CSI-RS or TP-RS list and/or a reporting configuration;    -   One or more heretofore undefined purposes are contemplated in a        reporting configuration, reportConfig. One purpose, for example,        may correspond to a purpose set to “reportMeasCSI_RS”.        Embodiments contemplate that when a reporting configuration with        purpose set to “reportMeasCSI_RS” may be received by a WTRU, the        WTRU may perform measurements on the reference signals of the        transmission points (e.g. CSI-RS or TP-RS). The report        configuration may include an event triggered configuration with        an additional purpose and/or identifier that this report        configuration may be used for CSI-RS measurement. The report        configuration may be used to request the WTRU to measure the        listed CSI-RS and report them within a configured time period,        for example;    -   The measurement object may include the transmission point CSI-RS        or TP-RS configuration (e.g. the list of transmission points to        perform CSI-RS or TP-RS measurements). When referred to        hereafter, this list may be referred to as        “pointsForWhichToReportMeasCSI_RS” and the configuration may be        according to any of the configuration described previously;        and/or    -   The reporting configuration may contain the        “pointsForWhichToReportMeasCSI_RS” information.

Embodiments contemplate that the reporting configuration may be used inconjunction with any of the techniques described previously to configurethe WTRU with measurement criteria (e.g. events). When the criteria forthe associated event(s) may be met for the transmission points in thelist a measurement report may be triggered. In one or more embodiments,the WTRU may be requested to measure and/or report a set of transmissionpoints, by way of, for example, a one shot request for transmissionpoint measurements. For example, this may be achieved by using thereporting configuration (e.g. reportConfig). Embodiments contemplatethat the one or more heretofore undefined purpose described previously(reportMeasCSI_RS) may be used to indicate to the WTRU to performmeasurements on the configured transmission point list and, in someembodiments, to report them. The reportConfig may set the purpose toreportMeasCSI_RS and may or may not configure an event trigger for thegiven configuration. The WTRU may report the measurements, perhaps assoon as some or all requested transmission points may be measured or maysend the report after a configured period of time, for example. In oneor more embodiments, at the expiration of a timer the WTRU may reportsome or all measured and/or detected CSI-RS.

In one or more embodiments, the transmission point or CSI-RS to measurelist may be provided as part of a measurement object (e.g. theintra-frequency measurement object). The measurement object may includea list of CSI-RS, TP-RS, and/or transmission points that the WTRU maymeasure, and in one or more embodiments perhaps should measure. Whenreferred to hereafter, this list may be referred to aspointsForWhichToReportMeasCSI_RS. In such an example, the reportingconfiguration may include a report type or purpose (e.g.reportMeasCSI_RS) and may further contain a reporting criteria, whereina reporting criteria may include an existing event (e.g. event 4) or aheretofore undefined event. Alternatively or additionally, the reportconfiguration may set the purpose to “reportMeasCSI-RS” (and in someembodiments perhaps may only set the purpose to “reportMeasCSI-RS”) andmay not configure an event. In such a case, the WTRU may use thepresence of such report purpose to indicate that it may measure and mayacquire (or at least attempt to acquire) the transmission point CSI-RSprovided and may report the measurement quantities once measured, orwithin a configured time, for example.

In one or more embodiments, the WRTU may be configured with at least onemeasurement identity for transmission point CSI-RS reporting that maycombine at least one of reportConfig with the purpose set to“reportMeasCSI_RS” and/or a corresponding measurement object (e.g.containing the CSI-RS configuration, pointsForWhichToReportMeasCSI_RS).

In one or more embodiments, for some or each measId, embodimentscontemplate that the corresponding reportConfig may include a purposeset to “reportMeasCSI_RS”. In some embodiments, the WTRU may performmeasurements on the CSI-RS on the frequency in the associatedmeasObject. For example, in case no assistant information on the CSI-RSmay be provided to the WTRU, the WTRU may detect (or at least attempt todetect) CSI-RS on a configured subframe, perhaps on the known possibleresource elements for CSI-RS for a given antenna configuration and maymeasure the configured measurement quantity (e.g. RSRP). By way offurther example, the WTRU may perform measurements on transmissionpoints CSI-RS or TP-RS found in cellForWhichToReportMeasCSI_RS.

In one or more embodiments, for some or each measId, embodimentscontemplate that the corresponding reportConfig may include a purposeset to reportMeasCSI_RS. In some embodiments, the WTRU may consider anytransmission point (CSI-RS) detected on the given cell, matching thevalue of the “cellForWhichToReportMeasCSI_RS” that may be included inthe corresponding measObject within the VarMeasConfig to be applicablefor event reporting and/or triggering provided in the correspondingReportConfig.

In one or more embodiments, a heretofore undefined measurement objectmay be configured in the WTRU. The measurement object may containpointsForWhich ToReportMeasCSI_RS. At least one measurement identity maybe configured in which such measurement object and/or a reportingconfiguration may be linked, perhaps in order to allow the WTRU to takemeasurements on transmission points for the serving cell and/or anyother cell, for example, among other reasons. In one or moreembodiments, for some or each measID, the corresponding measurementobject may have a cellForWhich ToReportMeasCSI_RS included. Embodimentscontemplate that the WTRU may consider any transmission point (CSI-RS)that may be detected on the given cell, and may match the value of the“cellForWhichToReportMeasCSI_RS” that may be included in thecorresponding measObject within the VarMeasConfig to be applicable forevent reporting and/or triggering provided in the correspondingReportConfig.

Embodiments contemplate autonomous removal of a measurementconfiguration. In one or more embodiments, for example where thetransmission points to measure may correspond to transmissions pointspresent in the serving cell (and in some embodiments perhaps in theserving cell only), the WTRU may autonomously remove one or moremeasurement configurations, for a number of reasons, such as when aserving cell change may occur. By way of further example, embodimentscontemplate that a change of serving cell and/or a handover may occur,where the WTRU may autonomously remove one or a combination of thefollowing measurement configurations:

-   -   The measurement identity with a corresponding reportConfig that        may have the purpose set to “reportMeasCSI_RS”;    -   The measurement identity with a corresponding measObject that        may have a CSI-RS list to measure (e.g. this may be used where a        heretofore undefined measurement object may be introduced for        CSI-RS measurement purpose);    -   The reportConfig with purpose set to reportMeasCSI_RS; and/or        The cellForWhichToReportMeasCSI_RS may be removed from the        memory of the WTRU for the given measurement object.

When the criteria corresponding to one of the measurement events (e.g.report configurations) for a transmission point may be fulfilled and/orwhen the WTRU may determine to transmit a measurement report accordingto a request within a reporting configuration. The WTRU may trigger ameasurement report wherein some or all of the following information maybe included and sent to the network: the measurement identity; thephysical channel identity of the serving cell; the transmission point(s)identity that triggered the event and the corresponding measurementresult, where the transmission point identity may correspond to atransmission point index provided in the original configuration message,which may be an explicit index or implicitly determined by the WTRUbased on the order of the transmission point configuration(alternatively, the transmission point identity may be indicated in thereport by way of providing the virtual cell ID that may be provided aspart of the measurement list, for example for the scenario where avirtual ID may be provided for the WTRU—the transmission point identitymay include the TSI and/or the PI); the subset in which the CSI-RS orTP-RS that trigger the event may correspond; and/or the measurements ofother transmission points may also be included in the report. In case ofblind detection, embodiments contemplate that the RE in which areference signal may have been detected may be indicated in the report.The network may use this measurement report to determine the CoMP setand configure the WTRU with a set, which may determine the set oftransmission points for which the WTRU may perform CSI reporting. One ormore embodiments may be equally extended to transmission points in aSecondary serving cell (Scell), wherein in some embodiments a specificScell offset may also be defined.

Alternatively or additionally, the WTRU may be configured with multiplepoints in its CoMP Resource Management Set which may not belong to thecoordinating cluster of points that the WTRU may be currently beingserved with. Furthermore, the network may configure an offset value tobe used for such points, and in some embodiments perhaps only for suchpoints. One or more embodiments contemplate that when an event occurswith respect to these points (e.g., based on measurements and/or the useof the offset) the WTRU may report a full set of measurements to thenetwork. Alternatively or additionally, the WTRU may report a single bitflag to indicate that the received power of a point outside of thecoordinating cluster, but in the CoMP Resource Management Set, hastriggered the event. This can be used as a trigger for the network toconfigure the WTRU to take more measurements for a number of reasons,such as for example to enable mobility. Alternately or additionally,this event can be used by the network to trigger UL enhanced inter-cellinterference cancellation with the corresponding point. One or moreembodiments contemplate that these techniques could be used to minimizepossible UL interference caused by WTRUs close to transmission pointslocated outside of its coordinating cluster.

Embodiments contemplate the measurement of CSI-RS of one or moredifferent subsets of transmission points. In one or more embodiments,the WTRU may measure a set of CSI-RS associated to differenttransmission points (or subset thereof) in different subframes. Thesubframes during which the WTRU may measure the set of CSI-RS of aspecific subset of transmission points may occur on a periodic basis. Inthis case, the periodicity and/or offset of the subframes during whichCSI-RS may be measured may be different for some or each subset oftransmission points. In one or more embodiments, the WTRU may measurethe CSI-RS reference signals of a transmission point according to asubframe configuration (I_(CSI-RS) and/or subframeConfig parameter),and/or a number of antennas (antennaPortsCount parameter) specific tothis transmission point. In other words, the WTRU may be provided withmore than one non-zero-power CSI-RS configuration instead of, forexample, a single one. This technique may allow for more flexibility forthe configuration of the CSI-RS transmission in a network including alarge number of transmission points in the same geographical area, forexample.

The WTRU may also be provided with a set of zero-power CSI-RS (or mutingpattern) for some or each transmission point (or subset thereof),occurring in different subframes for different transmission points (orsubset thereof). The WTRU may utilize the knowledge of the existence ofthese muting patterns for at least the following purposes: PDSCHdecoding; and/or CSI calculation adjustment, such as interferenceestimation and/or estimation of desired signal occurring in the sameOFDM symbols as a muted resource element, for example. In one or moreembodiments, there may be a muting pattern (and in some embodimentsperhaps a single muting pattern) defined for the purpose of estimatinginterference for some or all types of CQI, or separate muting patternsdefined for the purpose of estimating interference for some or each typeof CQI, such as aggregated CQI, per-point CQI without muting assumptionin other points, and/or per-point CQI with muting assumption in otherpoints.

In one or more embodiments, the WTRU may measure a set of CSI-RSassociated to different transmission points in the same subframe but indifferent resource elements. This technique may have the benefit thatthe phase difference between transmission points can be more accuratelymeasured as the signals are measured in the same subframe, for example.

More specifically, in one or more embodiments, the CSI-RS associated todifferent transmission points may be transmitted and/or measured by theWTRU in different OFDM symbols in the time domain. Such embodiments mayminimize issues that may stem from an imbalance of received powerbetween the signals transmitted from different transmission points towhich the path loss may be different. In some embodiments, the WTRU maymeasure the CSI-RS reference signals of a transmission point accordingto a CSI reference signal configuration (and/or a number of antennaports) specific to this transmission point instead of a CSI referencesignal configuration (resourceConfig parameter) that may be common tosome or all transmission points. Such reference signal configuration mayfor instance be indicated by an integer ranging from 0 to 31 for some oreach transmission point (for example), and may be provided by higherlayer or physical layer signaling.

FIG. 3A illustrates exemplary CSI-RS port mappings for normal CPsubframes. According to the number of TX antennas at the transmissionpoint, one set of the shown CSI-RS ports may be used for CSImeasurement. In some embodiments, perhaps only one set of the shownCSI-RS ports may be used for CSI measurement. One or more embodimentscontemplate that simultaneous CSI measurement of more than onetransmission point in the same subframe can be achieved. For example, ina multi-point transmission system including a Macro eNB with 4 Txantennas and 3 remote radio heads each equipped with 2 TX antennas,CSI-RS may be transmitted as shown in FIG. 3B. In FIG. 3B, the4-Resource-Element set shown (in the first and seventh rows of columns10 and 11) may be used for the CSI measurement of the Macro eNB. Thethree 2-Resource-Element sets shown (for example, in the third row ofthe fifth and sixth columns of 2 CSI-RS ports and 4 CSI-RS ports; in thethird row of the twelfth and thirteenth columns of 4 CSI-RS ports) maybe used for CSI measurements of the three remote radio heads, such asremote radio heads A, B, and/or C. The WTRU may be configured to measurethe CSI-RS transmitted from the macro eNB and the CSI-RS transmittedfrom at least one of the remote radio heads. Since these may betransmitted in different OFDM symbols, there may be no measurementdegradation due to potential power imbalance between the CSI-RStransmitted from these two nodes.

In one or more embodiments, the CSI-RS may be transmitted and/orreceived by the CoMP-capable WTRU during specific subframes (and in someembodiments perhaps only during specific subframes), which may bedefined as “multi-port measurement” sub-frame, and whose pattern may beprovided by higher layers. In some embodiments, such sub-frames may beincluded as a subset of MBSFN-subframes to prevent legacy WTRU's fromattempting to perform certain measurements and related processing inthese subframes.

In one or more embodiments, different transmission points (or subsetsthereof) may be associated with different values of the ratio of PDSCHEPRE to CSI-RS EPRE (or p-C parameter) which may be used at least toderive the CQI. At times, or in some embodiments whenever, the WTRU mayestimate the CSI associated to a given transmission point (or subsetthereof), the WTRU may determine the appropriate value of the ratio forthis transmission point (or subset thereof) and may use it to calculatethe CSI. The value of the ratio for each transmission point, or subsetthereof may be provided by higher layers (e.g. RRC signaling). In one ormore embodiments where the WTRU may estimate CSI based on at least onecommon reference signal (CRS), the WTRU may estimate the CSI associatedto a given transmission point by using a value of the cell-specific RSEPRE (parameter referenceSignalPower) specific to this transmissionpoint, for example.

In light of the descriptions herein, and referring to FIG. 4, exemplaryembodiments contemplate a wireless transmit/receive device (WTRU) thatmay be configured, at least in part, at 402, to identify one or moretransmission points. The one or more transmission points may beconfigured for channel state information (CSI) reporting. The WTRU maybe further configured, at 404, to generate CSI for the one or moretransmission points. Also, the WTRU may be configured, at 406, to sendthe CSI to one or more nodes in communication with the WTRU. Embodimentscontemplate that the one or more transmission points may include atleast one antenna port in communication with the WTRU. Embodiments alsocontemplate that the one or more transmission points may be CSIreference signal (CSI-RS) resources. Embodiments contemplate that, at408, the WTRU may be further configured to receive an indication of theone or more transmission points via signaling from one or more logicallayers higher than a physical layer of the WTRU.

Embodiments contemplate that the WTRU, at 410, may be further configuredto determine the one or more transmission points based, at least inpart, on at least one characteristic of a signal that may be transmittedrespectively from the one or more transmission points. Embodimentscontemplate that the at least one characteristic may be at least one ofsignal strength, signal quality, or channel quality, for example.Embodiments also contemplate that the WTRU may, at 412, be furtherconfigured to identify one or more subsets of the one or moretransmission points. Embodiments contemplate that the one or moretransmission points may be further configured for CSI reporting in oneor more subframes. Embodiments contemplate that the WTRU may, at 414, befurther configured to send the CSI for at least one subset in at leastone subframe. Embodiments contemplate that the at least one subframe maybe determined based, at least in part, on at least one of a system framenumber or a subframe number. Embodiments also contemplate that the WTRUmay, at 416, be further configured to send the CSI for at least onesubset in at least one subframe in at least one of a periodic manner oran aperiodic manner.

Embodiments contemplate one or more methods that may be performed by awireless transmit and receive unit (WTRU). Referring to FIG. 5, one ormore embodiments may include, at 502, identifying K transmission points,where the K transmission points may be configured for channel stateinformation (CSI) reporting, and where K may be an integer. Embodimentsmay further include, at 504, generating CSI for one or more of the Ktransmission points. In addition, embodiments may include, at 506,sending the CSI to one or more nodes in communication with the WTRU.Also, embodiments may include, at 508, receiving at least one of a CSIreference signal (CSI-RS) or a common reference signal (CRS) that may betransmitted respectively by the K transmission points. Embodimentscontemplate that the identifying the K transmission points may be based,at least in part, on the received CSI-RS or CRS. In one or moreembodiments, the generating the CSI may, at 510, include generating atleast one of a joint rank indication or a per-point rank indication forthe one or more of the K transmission points. In one or moreembodiments, the generating the CSI may, at 512, include generating ajoint channel quality index (CQI), where the joint CQI may correspond toa joint transmission over the one or more of the K transmission points.

Embodiments contemplate that the joint transmission over the one or moreof the K transmission points may be that of at least one codeword.Embodiments also contemplate that the joint CQI may include at least oneof a coherent joint CQI or a non-coherent joint CQI, for example.Embodiments also contemplate that the generating the CSI may, at 514,include generating a precoding matrix indicator (PMI) for the one ormore of the K transmission points.

Referring to FIG. 6, embodiments contemplate a wireless transmit/receivedevice (WTRU) that may be configured, at least in part, at 602, toidentify one or more transmission points, where the one or moretransmission points may be configured for channel state information(CSI) reporting. At 604, the WTRU may be configured to determine atransmission state (or CSI process) for the one or more transmissionpoints. At 606, the WTRU may be configured to generate CSI for the oneor more transmission points. Also, at 608, the WTRU may be furtherconfigured to receive an indication of the transmission state (or CSIprocess) for the respective one or more transmission points, where theindication of the transmission state (or CSI process) may include one ormore of a transmitting state, an interfering state, a blanked state, oran unknown state, for example. At 610, the WTRU may be furtherconfigured to compare the determined transition state for the one ormore transmission points to a predetermined transition state for the oneor more transmission points. The WTRU may also, at 612, be configured tosend the CSI for respective one or more transmission points to one ormore nodes in communication with the WTRU upon the transmission state(or CSI process) of the respective one or more transmission points beingin the predetermined transmission state (or CSI process).

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

1-23. (canceled)
 24. A wireless transmit/receive unit (WTRU), the WTRUcomprising: a memory; and a processor, the processor configured at leastto: receive a first configuration information that indicates a first setof channel state information (CSI) reference signal (CSI-RS) resourcesand comprises a first non-zero-power (NZP) CSI-RS information thatindicates a first set of NZP CSI-RS resources and a first CSIinterference measurement (CSI-IM) information that indicates a first setof CSI-IM resources, the first configuration information furtherindicating a first assumed ratio of physical downlink shared channel(PDSCH) energy per resource element (EPRE) to a first NZP CSI-RS EPRE;receive a second configuration information that indicates a second setof CSI-RS resources and comprises a second NZP CSI-RS information thatindicates a second set of NZP CSI-RS resources and a second CSI-IMinformation that indicates a second set of CSI-IM resources, the secondconfiguration information further indicating a second assumed ratio ofPDSCH EPRE to a second NZP CSI-RS EPRE; in response to a determinationthat a first aperiodic CSI report associated with the first set ofCSI-RS resources has been triggered, send the first aperiodic CSI reportassociated with the first set of CSI-RS resources; and in response to adetermination that a second aperiodic CSI report associated with thesecond set of CSI-RS resources been triggered, send the second aperiodicCSI report associated with the second set of CSI-RS resources.
 25. TheWTRU of claim 24, wherein the first NZP CSI-RS information furtherindicates the first assumed ratio of PDSCH EPRE to the first NZP CSI-RSEPRE.
 26. The WTRU of claim 25, wherein the second NZP CSI-RSinformation further indicates the second assumed ratio of PDSCH EPRE tothe second NZP CSI-RS EPRE.
 27. The WTRU of claim 25, wherein the firstNZP CSI-RS information further indicates a set of resource elements, aperiodicity, and an offset.
 28. The WTRU of claim 24, wherein the firstCSI-IM information further indicates a set of resource elements, aperiodicity, and an offset.
 29. The WTRU of claim 24, wherein theprocessor is further configured such that the first aperiodic CSI reportis determined according to one or more aperiodic report modes configuredfor the first set of CSI-RS resources.
 30. The WTRU of claim 24, whereinthe processor is further configured to associate a rank indicator (RI)with the first set of CSI-RS resources.
 31. The WTRU of claim 30,wherein the processor is further configured to report a common RI valueassociated with the first set of CSI-RS resources and the second set ofCSI-RS resources.
 32. A method performed by a wireless transmit/receiveunit (WTRU), the method comprising: receiving, by the WTRU, a firstconfiguration information that indicates a first set of channel stateinformation (CSI) reference signal (CSI-RS) resources and comprises afirst non-zero-power (NZP) CSI-RS information that indicates a first setof NZP CSI-RS resources and a first CSI interference measurement(CSI-IM) information that indicates a first set CSI-IM resources, thefirst configuration information further indicating a first assumed ratioof physical downlink shared channel (PDSCH) energy per resource element(EPRE) to a first NZP CSI-RS EPRE; receiving, by the WTRU, a secondconfiguration information that indicates a second set of CSI-RSresources and comprises a second NZP CSI-RS information that indicates asecond set of NZP CSI-RS resources and a second CSI-IM information thatindicates a second set of CSI-IM resources, the second informationfurther indicating a second assumed ratio of PDSCH EPRE to a second NZPCSI-RS EPRE; sending, by the WTRU, a first aperiodic CSI reportassociated with the first set of CSI-RS resources in response to adetermination that the first aperiodic CSI report associated with thefirst set of CSI-RS resources has been triggered; and sending, by theWTRU, a second aperiodic CSI report associated with the second set ofCSI-RS resources in response to a determination that the secondaperiodic CSI report associated with the second set of CSI-RS resourceshas been triggered.
 33. The method of claim 31, wherein the first NZPCSI-RS information further indicates the first assumed ratio of PDSCHEPRE to the first NZP CSI-RS EPRE.
 34. The method of claim 32, whereinthe second NZP CSI-RS information further indicates the second assumedratio of PDSCH EPRE to the second NZP CSI-RS EPRE.
 35. The method ofclaim 32, wherein the first NZP CSI-RS information further indicates aset of resource elements, a periodicity, and an offset.
 36. The methodof claim 31, wherein the first CSI-IM information further indicates aset of resource elements, a periodicity, and an offset.
 37. The methodof claim 31, wherein the determination that the first aperiodic CSIreport associated with the first set of CSI-RS resources has beentriggered comprises using one or more aperiodic report modes configuredfor the first set of CSI-RS resources.
 38. The method of claim 31, themethod further comprising associating a rank indicator (RI) with thefirst set of CSI-RS resources.
 39. The method of claim 36, the methodfurther comprising reporting a common RI value associated with the firstset of CSI-RS resources and the second set of CSI-RS resources.
 40. Awireless transmit/receive unit (WTRU), the WTRU comprising: a memory;and a processor, the processor configured at least to: receive a firstconfiguration information that indicates a first set of channel stateinformation (CSI) reference signal (CSI-RS) resources and comprises afirst non-zero-power (NZP) CSI-RS information that indicates a first setof NZP CSI-RS resources and a first CSI interference measurement(CSI-IM) information that indicates a first set of CSI-IM resources, thefirst NZP CSI-RS information further indicating a first assumed ratio ofphysical downlink shared channel (PDSCH) energy per resource element(EPRE) to a first NZP CSI-RS EPRE; receive a second configurationinformation that indicates a second set of CSI-RS resources andcomprises a second NZP CSI-RS information that indicates a second set ofNZP CSI-RS resources and a second CSI-IM information that indicatesecond set of CSI-IM resources, the second NZP CSI-RS informationfurther indicating a second assumed ratio of PDSCH EPRE to a second NZPCSI-RS EPRE; in response to a determination that a first aperiodic CSIreport associated with the first set of CSI-RS resources has beentriggered, send the first aperiodic CSI report associated with the firstset of CSI-RS resources; and in response to a determination that asecond aperiodic CSI report associated with the second set of CSI-RSresources has been triggered, send the second aperiodic CSI reportassociated with the second set of CSI-RS resources.
 41. The WTRU ofclaim 38, wherein the first NZP CSI-RS information further indicates aset of resource elements, a periodicity, and an offset.
 42. The WTRU ofclaim 38, wherein the first CSI-IM information further indicates a setof resource elements, a periodicity, and an offset.
 43. The WTRU ofclaim 38, wherein the processor is further configured such that thefirst aperiodic CSI report is determined according to one or moreaperiodic report modes configured for the first set of CSI-RS resources.